| Rederiaktiebolaget Hildegaard | Transport & logistics | 1935 |
| Refuture Ventures Ab, Mariehamn | Information & communication | 2006 |
| Rehab City Ab | Health & social care | 2018 |
| Rendicon Oy | Arts & recreation | 2004 |
| Renovator Mariehamn Ab | Construction | 2007 |
| Respond4You Ab | Professional & scientific | 2005 |
| Restaurang Nautical Ab | Hospitality | 2004 |
| Restoreit Finland, filial | Wholesale & retail | 2020 |
| Revisa Ab | Professional & scientific | 1991 |
| Revisum Oy Ab | Professional & scientific | 2025 |
| Rickert-Olsson konsulter AB | Health & social care | 2020 |
| Rofast Ab | Real estate | 2006 |
| Rollic Ab | Wholesale & retail | 1987 |
| Rosenbergs Trafikskola Ab | Education | 2020 |
| Rosenblad's Ab | Agriculture & fishing | 1985 |
| Rosjö Ab | Administrative & support | 2022 |
| Rostedt Holding AB | Real estate | 2022 |
| Rosteriverket AB | Manufacturing | 2021 |
| Roundnet Camps by Beeks Ab | Arts & recreation | 2025 |
| Royal Pizza & Grill öppet bolag | Hospitality | 2018 |
| Royal Svets och Bygg Kb | Construction | 2012 |
| Rundbergs Bil & Service Ab | Wholesale & retail | 1978 |
| Rundhusbyn Ab | Hospitality | 2020 |
| Rundqvist Invest Ab | Financial services | 2022 |
| Ruohoinenmäki Renewables Oy | Energy | 2023 |
| Rustik Åland Ab | Manufacturing | 2011 |
| RÖF-Invest Ab | Financial services | 2003 |
| Rökeri Kiosken Ab | Wholesale & retail | 2002 |
| Rönnhem Ab | Real estate | 2019 |
| Rörteamet by LITA Group Ab | Construction | 2024 |
| Rörteamet Åland Ab | Construction | 2025 |
| S Widesköld Ab | Health & social care | 2025 |
| S-Crosskey Ab | Information & communication | 2005 |
| S-Z Dental Ab | Health & social care | 2021 |
| SABA Wind Oy Ab | Energy | 2004 |
| SAJ Instrument Ab | Manufacturing | 1980 |
| SAL Fastigheter Ab | Real estate | 2020 |
| SAT Ab (Sjölund Arkitektur och Teknik Aktiebolag) | Construction | 2001 |
| SC Capital Ab | Professional & scientific | 2006 |
| SG Capital Ab | Financial services | 2022 |
| SH Ståhl Konsult Ab | Financial services | 2006 |
| SIOS system Ab | Professional & scientific | 2025 |
| Smvo AB | Professional & scientific | 2022 |
| SNBLL Software Ab | Information & communication | 2019 |
| STEN Skomakeri Ab | Other services | 2019 |
| Storfors & Co AB | Hospitality | 1992 |
| SVS Åland Ab | Administrative & support | 2022 |
| Saarinen & Åkerblom Ab | Manufacturing | 1975 |
| Sagojord Nordisk Scenkonst AB | Arts & recreation | 2019 |
| Saku Medical Ab | Health & social care | 2019 |
| Sales Dynamic International Ab (S.D.I.) | Wholesale & retail | 1993 |
| Sally Ab | Transport & logistics | 1985 |
| Salon Locky Kommanditbolag | Other services | 1998 |
| Salong Cut Ab | Other services | 2016 |
| Salt Konsthantverk Ab | Wholesale & retail | 2002 |
| Saltö Ab | Construction | 2017 |
| Sama Dental Ab | Health & social care | 2006 |
| Samba Media Group Ab | Professional & scientific | 2010 |
| Sandåsen Arts and Crafts öppet bolag | Wholesale & retail | 2011 |
| Sane Redovisning Ab | Professional & scientific | 2025 |
| Sartoriale Öppet bolag | Wholesale & retail | 2006 |
| Savantone Invest Ab | Financial services | 2007 |
| Sax Man Ab | Other services | 2006 |
| Scandenergy Contracting Ab | Professional & scientific | 1989 |
| Scandibygg Ab | Construction | 2017 |
| Schaumans Redovisning Ab | Professional & scientific | 2020 |
| Scila AB Filial i Finland | Professional & scientific | 2026 |
| Scintilla Ab | Health & social care | 2021 |
| Sea Lines Operations Ab Ltd | Transport & logistics | 2024 |
| Sea Lines Services Finland Oy | Transport & logistics | 2010 |
| Sea Lines Shipping Finland Oy | Transport & logistics | 2010 |
| Sea Meadow AB | Professional & scientific | 2005 |
| Seabris Ab | Education | 2020 |
| Seamlessales Holding AB | Administrative & support | 2024 |
| Seb Capital Ab | Financial services | 2025 |
| Selecta Mariehamn Ab | Wholesale & retail | 1994 |
| Serendio Ab | Financial services | 2023 |
| Servermapper Ab | Information & communication | 2010 |
| Sharebook Ab | Financial services | 2017 |
| Sigges Verkstad Ab | Other services | 2022 |
| Silva Capital Ab | Financial services | 2015 |
| Silverskär Ab | Administrative & support | 1981 |
| Simbelmyne Ab | Financial services | 1995 |
| Simon Larsson Elkonsult AB | Professional & scientific | 2024 |
| Sindéns Marin & Service AB | Transport & logistics | 2025 |
| Sire Forest Ab Ltd | Transport & logistics | 2010 |
| Sire Securities Ab | Financial services | 1990 |
| Sixtens Grävtjänst Ab | Construction | 2006 |
| Sjöstrand Förvaltning Ab | Professional & scientific | 2009 |
| Skagul Invest Ab | Financial services | 2011 |
| Skalia öppet bolag | Wholesale & retail | 2013 |
| Skandinavien Water Systems Aktiebolag filial Åland | Wholesale & retail | 2011 |
| Skandinavisk Byggkonsult Ab | Professional & scientific | 2016 |
| Skinnars Arkitektur Ab | Professional & scientific | 2025 |
| Skylten Reklamaktiebolag | Information & communication | 2019 |
| Skönhetsmagasinet Åland Ab | Other services | 2018 |
| Slätholms avloppsandelslag | Water & waste | 2025 |
| Smakverket Ab | Hospitality | 2011 |
| Snax Ab | Hospitality | 2023 |
| Snellman Investment Ab | Hospitality | 1984 |