| JE Grafix Ky | Professional & scientific | 2014 |
| JFT Parts Rotors Oy | Wholesale & retail | 2009 |
| JH-Puu Ky | Agriculture & fishing | 2012 |
| JHE-Logistiikka Oy | Transport & logistics | 2018 |
| JHMK-Kiinteistöpalvelut Oy | Real estate | 1989 |
| JJH-Logistiikka oy | Transport & logistics | 2018 |
| JJM Global Trade Ky | Wholesale & retail | 2006 |
| JJP Herkut Oy | Manufacturing | 2013 |
| JK Advisory & Consulting Oy | Professional & scientific | 2024 |
| JK Talotekniikka Oy | Construction | 2017 |
| JKV-Sähkö Oy | Construction | 2008 |
| JLH Invest Oy | Construction | 2008 |
| JM Rakennuttajapalvelu Oy | Professional & scientific | 2024 |
| JMSN Oksanen Oy | Wholesale & retail | 2014 |
| JOTA Group Osk | Administrative & support | 2014 |
| JP Finance Oy | Construction | 2023 |
| JPH Invest Oy | Real estate | 2021 |
| JR&MR Trading Oy | Wholesale & retail | 2008 |
| JR-Kuljetus Ky | Transport & logistics | 1990 |
| JRT Consulting Oy | Professional & scientific | 2020 |
| JRV Invest Oy | Real estate | 2019 |
| JS-Service ky | Other services | 2004 |
| JV-Teknopalvelu Oy | Wholesale & retail | 1992 |
| Jyri Mäkinen Ky | Hospitality | 2004 |
| Jakendos Oy | Professional & scientific | 2001 |
| Jaletec oy | Construction | 2026 |
| Jalo Huoneistot Oy | Real estate | 2022 |
| Japa-Rakenne Oy | Professional & scientific | 2010 |
| Jarmolan Kiinteistö Oy | Real estate | 1993 |
| Jarron Oy | Information & communication | 1990 |
| Jaskatec Ky | Wholesale & retail | 1986 |
| Jedu Ky | Construction | 1990 |
| Jeremus Oy | Financial services | 1992 |
| Jilotek Ky | Wholesale & retail | 1983 |
| Jmak Oy | Wholesale & retail | 2016 |
| Joka Oy Kouvola | Real estate | 2009 |
| Jokelan Automyynti Oy | Wholesale & retail | 2016 |
| JopAir OY | Administrative & support | 2022 |
| Juha Kalervo Bergman Oy | Wholesale & retail | 1991 |
| Juha Lyijynen Oy | Transport & logistics | 1996 |
| Juliasys Studio Oy | Professional & scientific | 2025 |
| Julkisivumaalaus ja -saneeraus JMS Ky | Construction | 1997 |
| Juninet Oy | Other services | 2022 |
| Jyri Paavola Oy | Hospitality | 2012 |
| Jyritys Oy | Real estate | 2022 |
| Jyrki Pakkanen Ky | Transport & logistics | 1999 |
| Jyräänkoski-Hyppälä vesihuolto-osuuskunta | Water & waste | 2003 |
| K-A Digiworks Oy | Professional & scientific | 2024 |
| K-Weld Oy | Manufacturing | 2017 |
| K. Beauty & Design Oy | Other services | 2025 |
| KAJO kaluste Oy | Wholesale & retail | 2024 |
| Kalansilmä OY | Information & communication | 2009 |
| KAMU Clothing Oy | Wholesale & retail | 2024 |
| KATTO JES Oy | Construction | 2015 |
| KET Invest Oy | Construction | 2016 |
| KF sähköpalvelu OY | Manufacturing | 2015 |
| KH Elsa Group Oy | Health & social care | 2024 |
| KJI-Musiikki Kommandiittiyhtiö | Wholesale & retail | 1989 |
| KK Exploder Oy | Professional & scientific | 2023 |
| KK Kattohuolto Oy | Construction | 2022 |
| KK-Beyond Oy | Hospitality | 2024 |
| KLU Kattohuolto Oy | Construction | 2026 |
| KM Valoa kohti Oy | Hospitality | 2012 |
| KOU Palvelu Oy | Administrative & support | 2002 |
| Kovir OY | Real estate | 2021 |
| KOY Kouvolan Teletalo | Real estate | 2024 |
| KOY Kouvolan Yrittäjänkatu 17 | Real estate | 2019 |
| KPH-Logistiikka Oy | Transport & logistics | 2018 |
| KPT Group Oy | Wholesale & retail | 1978 |
| KRT-Karvio Oy | Real estate | 2007 |
| KSS Energia Oy | Energy | 1992 |
| KSS Verkko Oy | Energy | 2005 |
| KVL Jave Trading Oy | Wholesale & retail | 1997 |
| KVL Putki- ja Poltinhuolto Oy | Construction | 2011 |
| KVL Sähköpalvelu Oy | Construction | 2023 |
| KaaKau Oy | Transport & logistics | 2018 |
| Kaakko Festivals Oy | Arts & recreation | 2017 |
| Kaakkois-Suomen Metsätilat Oy LKV | Real estate | 2001 |
| Kaakkois-Suomen Osuuspankki | Financial services | 1992 |
| Kaakkois-Suomen Sähköpalvelu Oy | Construction | 1979 |
| Kaakkois-Suomen Tieto Oy | Information & communication | 2010 |
| Kaakkois-Suomen terminaalipalvelut Oy | Transport & logistics | 2025 |
| Kaakon Cargo Ky | Transport & logistics | 2008 |
| Kaakon Kori Oy | Other services | 2010 |
| Kaakon Rantavaruste Oy | Construction | 2015 |
| Kaakon Sammutinhuolto Oy | Manufacturing | 2023 |
| Kaarnasydän Oy | Wholesale & retail | 2012 |
| Kahden hullun matka Oy | Administrative & support | 2024 |
| Kahvila Riitta Karhu Ky | Hospitality | 1999 |
| Kahvila-Ravintola Anrié Ky | Hospitality | 1999 |
| Kaivuliike Veljekset Isaksson | Construction | 1986 |
| Kalalampi Holding Oy | Administrative & support | 2020 |
| Kalevala Plus Oy | Hospitality | 2011 |
| Kaliruha Foods Oy | Hospitality | 2022 |
| Kallion Creations Oy | Information & communication | 2019 |
| Kamons Oy | Other services | 2020 |
| KamuSta Oy | Real estate | 2020 |
| Kanava & Hormi Oy | Administrative & support | 2018 |
| Kapet Oy | Real estate | 2022 |
| Kara Holding Oy | Real estate | 2021 |