| Jaalan Sora ja Kuljetus Ky | | 1962 |
| Jaken Pölli Oy | Agriculture & fishing | 2020 |
| Jaken Sijoitukset Oy | Real estate | 2024 |
| Jakira Oy | Construction | 2004 |
| Jalo Ravintolat Oy | Hospitality | 2019 |
| Jalotakka Oy | Construction | 1984 |
| Jamra OY | Professional & scientific | 2016 |
| Japero Oy | Real estate | 2023 |
| Jari Hartikka Oy | Manufacturing | 1996 |
| Jari Huusari Ky | Wholesale & retail | 1995 |
| Jarjon Oy | Administrative & support | 2021 |
| Jarmo R Mulari Oy | Real estate | 1990 |
| Jens Transfer & Service Oy | Transport & logistics | 2019 |
| Jercom Yhtiö Ky | Wholesale & retail | 1991 |
| Jerejulius Oy | Professional & scientific | 2021 |
| Jiangsu Installation (Finland) Oy | Manufacturing | 2025 |
| Jokilaakson Louhinta Oy | Construction | 2004 |
| Jonnicon Heider Oy | Administrative & support | 2009 |
| Joomik Oy | Health & social care | 2020 |
| Jorma Orasvuo Oy | Professional & scientific | 1983 |
| Jotura Ky | Construction | 1988 |
| Judicor Oy | Information & communication | 1995 |
| Juha Lustig Ky | Wholesale & retail | 2004 |
| Juhani Haavisto Oy | Manufacturing | 1987 |
| Juju Visual Desire Oy | Professional & scientific | 2017 |
| Jukka Salomaa Oy | Wholesale & retail | 1996 |
| Jura Capital Oy | Financial services | 2024 |
| Jura Law Oy | Professional & scientific | 2019 |
| Jussin Kioski Ky | Wholesale & retail | 1987 |
| Jussin tiimi Oy | Professional & scientific | 2022 |
| Jylpyn Automaalaus Oy | Other services | 1995 |
| Jyrkilä Oy | Professional & scientific | 2005 |
| Jyrkilä Oy Kiinteistöt | Real estate | 2005 |
| Järvelän Tila & Kone Oy | Agriculture & fishing | 2020 |
| Järvinen Capital Oy | Real estate | 2018 |
| K & K rakentajat Oy | Construction | 2015 |
| K. Hostikka Oy | Construction | 2025 |
| K. Nygren Oy | Other services | 2010 |
| K/S FINLAND RETAIL II, filial i Finland | Real estate | 2007 |
| K2 Racing Team Oy | Arts & recreation | 2017 |
| KAK Service Oy | Other services | 2026 |
| KANTEK Oy | Professional & scientific | 2018 |
| KAP-Engineering Oy | Manufacturing | 1987 |
| Kapgroup OY | Real estate | 2013 |
| KARPOT-TV Oy | Information & communication | 2020 |
| KAT S Cafe OY | Hospitality | 2018 |
| KCY Oy | Real estate | 2008 |
| KHP Kiinteistöjen Huoltopalvelu Oy | Administrative & support | 2006 |
| KHR-sähkö Avoin yhtiö | Construction | 1992 |
| KK-Metalli Oy | Construction | 2008 |
| KL-Kuljetuspalvelut Oy | Transport & logistics | 2004 |
| Koirahuolto Hopeatassu Ky | Other services | 2013 |
| Koocee Invest OY | Health & social care | 2020 |
| Kotkan Laite-Asennus OY | Manufacturing | 2012 |
| Kotkan Ukkometsot OY | Real estate | 2011 |
| KP-Kodinkonepalvelu Ky | Other services | 2002 |
| KP-Teknik Oy | Wholesale & retail | 2016 |
| KPS-Finland Oy | Financial services | 2013 |
| KRH Service Oy | Other services | 2023 |
| KRK Engineering Oy | Professional & scientific | 2018 |
| KS-Siivous Ky | Administrative & support | 1983 |
| KST Plus Oy | Health & social care | 2014 |
| KTH Service Oy | Manufacturing | 2017 |
| KTP-Basket Oy | Arts & recreation | 2015 |
| KTT Tekniikka Oy | Wholesale & retail | 2012 |
| KTTYÖ Oy | Administrative & support | 2024 |
| KUITpalvelut Oy | Professional & scientific | 2024 |
| KVS Group Oy | Hospitality | 2025 |
| KW-Kalustus Avoin yhtiö | Construction | 1996 |
| Kymen Infratekniikka OY | Construction | 2012 |
| KYN Invest Oy | Real estate | 2011 |
| Kaakkois-Suomen Teollisuuspalvelu Kastep Ky | Wholesale & retail | 2005 |
| Kaakon Autohuolto Oy | Other services | 2015 |
| Kaakon Curion Oy | Transport & logistics | 1997 |
| Kaakon Isännöintikolmio Oy | Real estate | 1977 |
| Kaakon Kiinteistökehitys Oy | Real estate | 2026 |
| Kaakon Kumipyörät Oy | Transport & logistics | 2009 |
| Kaakon Liikenneapu Oy | Education | 2026 |
| Kaakon Maininki Oy | Administrative & support | 2020 |
| Kaakon Palvelut Oy | Transport & logistics | 2019 |
| Kaakon Ruoka- ja Lihapalvelu Oy | Manufacturing | 2021 |
| Kaakon Teline Oy | Construction | 2024 |
| Kaakonmari Oy | Other services | 2022 |
| Kaanel Studios Oy | Information & communication | 2022 |
| Kaarniemen Ratsutila Oy | Arts & recreation | 2017 |
| Kaarniemen Vesiosuuskunta | Water & waste | 1998 |
| Kaarniemen koirametsä Oy | Arts & recreation | 2024 |
| Kaarolandia Oy | Wholesale & retail | 2024 |
| Kaihdintuote Padatsu ja Söder | | 1990 |
| Kaksipäinen kotka - Huma Ky | Hospitality | 2012 |
| Kaksnolla Oy | Manufacturing | 2005 |
| Kakspy Palvelut Oy | Health & social care | 2017 |
| Kala ja Konna Oy | Wholesale & retail | 2023 |
| Kalanjalostus Fi-Re Oy | Wholesale & retail | 1992 |
| Kalaravintola Möljä Oy | Hospitality | 2013 |
| Kalastuspiste Kotka Oy | Wholesale & retail | 2009 |
| KaleviTrading Ky | Wholesale & retail | 1999 |
| Kalle Kurvinen Ky | Professional & scientific | 1994 |
| Kampaamo-parturi Art of Hair and Beauty Oy | Other services | 2009 |
| Kangas Keidas Oy | Wholesale & retail | 1946 |