| Insinööritoimisto Hynninen Oy | Professional & scientific | 2009 |
| Insinööritoimisto Latokylä Oy | Professional & scientific | 1998 |
| Insinööritoimisto S. Sonninen Oy | Professional & scientific | 1984 |
| Inuse International Oy | Wholesale & retail | 1996 |
| Invoy Automation Oy | Real estate | 1988 |
| Iso Börje Holding Oy | Financial services | 2025 |
| Iso-Börje Kiinteistöt Oy | Real estate | 2025 |
| Isännöinti Sajor Oy | Real estate | 2009 |
| Itsepalveluvarasto Holvi Oy | Transport & logistics | 2011 |
| J J J Niemi Oy | Financial services | 1995 |
| J Lindberg Holding Oy Ltd | Financial services | 2022 |
| J&S Energy Oy | Construction | 2026 |
| J.A. Balance Oy | Professional & scientific | 2003 |
| J.A. Tuontiallas Oy | Wholesale & retail | 1988 |
| JAFA TALOTEKNIIKKA Oy | Construction | 2025 |
| JH-Cons Ky | Construction | 2006 |
| JHRakentamispalvelut Oy | Construction | 2020 |
| JJS Invest Oy | Construction | 2020 |
| JK MarineService Oy | Manufacturing | 2025 |
| JKS Trade Oy | Other services | 2015 |
| JL Koneurakointi ja kuljetus Oy | Construction | 2008 |
| JN Trading Oy | Wholesale & retail | 1996 |
| JN-Telecommunications Oy | Financial services | 1992 |
| JPE Ruoka-Merkos Oy | Financial services | 1997 |
| JPK Laatoitus Oy | Construction | 2016 |
| JSiren Consulting Oy | Professional & scientific | 2024 |
| JV Corporation Oy | Wholesale & retail | 2025 |
| JVV-Pharma Oy | Wholesale & retail | 2019 |
| Ja-Sa Pro OY | Other services | 2020 |
| Jakava Oy | Wholesale & retail | 2023 |
| Jake Urakointi Oy | Construction | 1999 |
| Janreho Oy | Financial services | 2019 |
| Japek Oy | Construction | 1989 |
| Javenture Oy | Real estate | 1991 |
| Jempire Oy | Administrative & support | 2020 |
| Jensen Marine Oy | Transport & logistics | 2020 |
| Ji-Li Oy | Hospitality | 2017 |
| Jobiteam Oy | Administrative & support | 2005 |
| Jouni & Ugis Trade Cars Oy | Wholesale & retail | 2019 |
| Junitek Oy | Manufacturing | 1977 |
| Jurvan turvakoti oy | Real estate | 2020 |
| Jussam holding Oy | Manufacturing | 2023 |
| Juucare Oy | Health & social care | 2020 |
| K&Y Holding Oy | Financial services | 2020 |
| K-Rakenne Oy | Construction | 2016 |
| K9 Finland Oy | Wholesale & retail | 2017 |
| KJS Palvelut Oy | Administrative & support | 2021 |
| KNI Consulting Oy | Professional & scientific | 2025 |
| KS Saneeraus Oy | Construction | 2023 |
| KSP Kaarina Oy | Construction | 2020 |
| Kaarinan Aquadata Oy | Professional & scientific | 1990 |
| Kaarinan Autokorjaamo Oy | Other services | 2025 |
| Kaarinan Autokoulu Oy | Education | 1972 |
| Kaarinan Autopalvelu Oy | Other services | 2008 |
| Kaarinan Autoveljet avoin yhtiö | Other services | 2015 |
| Kaarinan Burger Oy | Hospitality | 2002 |
| Kaarinan Eläinlääkäriasema Oy | Professional & scientific | 2022 |
| Kaarinan Fysiopiste Oy | Health & social care | 2012 |
| Kaarinan Health for You Oy | Wholesale & retail | 2015 |
| Kaarinan Kehitys Oy | Professional & scientific | 1992 |
| Kaarinan Kello ja Kultaliike Ky | Wholesale & retail | 1988 |
| Kaarinan Konevuokraus Oy | Administrative & support | 2005 |
| Kaarinan Kuljetus Oy | Transport & logistics | 2006 |
| Kaarinan Kuntosali Oy | Arts & recreation | 2025 |
| Kaarinan Lukko Oy | Construction | 2004 |
| Kaarinan MK-Infrapalvelu Oy | Professional & scientific | 2021 |
| Kaarinan Nuohous Oy | Administrative & support | 2020 |
| Kaarinan Palvelukiinteistöt Oy | Real estate | 1989 |
| Kaarinan Putkihuolto ja Saneeraus Oy | Construction | 2020 |
| Kaarinan Rakennus-Asennus Oy | Construction | 2003 |
| Kaarinan Rantaravintolat Oy | Hospitality | 2023 |
| Kaarinan Sisustuskulma OY | Wholesale & retail | 2018 |
| Kaarinan TR-Maalaus Oy | Construction | 2016 |
| Kaarinan Varaosa Oy | Wholesale & retail | 1988 |
| Kaarinan Veteraanipuisto Oy | Real estate | 2022 |
| Kaarinan Vuokrakiinteistöt Oy | Real estate | 2012 |
| Kaarinanseudun Hautaustoimisto Oy | Other services | 1994 |
| Kaarinantien Grilli Oy | Hospitality | 1994 |
| Kaarjoki Konepaja Oy | Manufacturing | 2010 |
| Kaarjoki Oy | Manufacturing | 2019 |
| Kaarre Development Oy | Real estate | 2023 |
| Kaisei Group Oy | Other services | 2013 |
| Kaislikontien laituriosuuskunta | Real estate | 2018 |
| Kaivuuliike J & R, avoin yhtiö | Construction | 1984 |
| Kaivuuliike J. Jokinen Oy | Construction | 1993 |
| Kaivuuliike J. Sirviö Ky | Construction | 1990 |
| Kallen auto ja traileri oy | Wholesale & retail | 2018 |
| Kaluste-Westma Ky | Manufacturing | 1981 |
| Karata Oy | Financial services | 2020 |
| Karmar Invest Oy | Professional & scientific | 2010 |
| Katariinan Kruunu Oy | Health & social care | 2011 |
| Kattohuoltosi Suomi Oy | Construction | 2026 |
| Kaukosenlaidalla Oy | Professional & scientific | 2021 |
| Kauppahuone Kuusiaho Oy | Wholesale & retail | 2012 |
| Kauppatalo Välskäri 15 Oy | Real estate | 1998 |
| Kawaii Suomi Oy | Wholesale & retail | 2024 |
| Kb Parlift Ky | Construction | 1984 |
| Keijo Rantamo Ky | Wholesale & retail | 1994 |
| Kerttu B Oy | Wholesale & retail | 2017 |
| Ketola Oy Kaarina | Wholesale & retail | 1967 |