| Kiinteistöyhtiö Puolanlaituri Oy | Real estate | 2007 |
| Kiinteistöyhtiö Ylärakkola Oy | Real estate | 1985 |
| Kiinteistöyhtymä Kari ja Petri Lindqvist | Real estate | 1994 |
| Kilpihovi Oy | Professional & scientific | 1985 |
| Kimto Markkinointi Oy | Wholesale & retail | 1995 |
| Kipinä Creative Oy | Professional & scientific | 2020 |
| Kirby Group Engineering (Finland) Oy | Construction | 2019 |
| Kirjanpito Huusari Ky | Professional & scientific | 1990 |
| Kirjanpitotoimisto Kotkan Tilipalvelu Oy | Professional & scientific | 1995 |
| Kirjaverkko Oy | Information & communication | 2020 |
| KirsiKoo Coaching Oy | Professional & scientific | 2024 |
| Kiuru Palvelut Oy | Other services | 2015 |
| Kiva Talo Oy rakennuspalvelu | Construction | 2016 |
| Kivelän Merikala Ky | Wholesale & retail | 1991 |
| Kivisalmen Satama Oy | Real estate | 1991 |
| Kivit Oy | Professional & scientific | 2003 |
| Klapiukki Oy | Wholesale & retail | 2025 |
| Klinik8 Oy | Health & social care | 2019 |
| KnowBody Oy | Education | 2024 |
| KoHu-Works Oy | Manufacturing | 2020 |
| Koirantähden Oy | Other services | 2015 |
| Koivulan kerho Oy | Real estate | 2025 |
| KolmeKasi group Oy | Transport & logistics | 2026 |
| Kolsin Vesivoimantuotanto Oy | Energy | 1995 |
| Kolsin Voima Oy | Energy | 2014 |
| Kompassio Oy | Professional & scientific | 2019 |
| Kona Oy | Financial services | 1989 |
| Konditoria Galette Oy | Manufacturing | 1989 |
| Konditoria SM-ER Oy | Manufacturing | 2023 |
| Kone Makkonen Oy | Wholesale & retail | 1982 |
| Kone ja Kuljetus Pukkila Oy | Construction | 2019 |
| Koneellinen Puhdistushuolto Sakka Oy | Water & waste | 1985 |
| Konekotka Oy | Wholesale & retail | 1991 |
| Koneurakoitsija J. Kierikka Ky | Construction | 1991 |
| Konkila Ky | Hospitality | 2011 |
| Konsultointi P.Aarnio Oy | Administrative & support | 2019 |
| Kopikot Oy | Information & communication | 2012 |
| Kopikot Russia Oy | Information & communication | 2013 |
| Kopioklubi Oy | Administrative & support | 1990 |
| Korela Works Oy | Other services | 2021 |
| KorelaBoats.com Oy | Manufacturing | 2020 |
| Korelan Kauppahuone Oy | Arts & recreation | 1995 |
| Koria Holding Oy | Water & waste | 2026 |
| Korkeakosken Kalamaja Oy | Hospitality | 2022 |
| Koskelontien Kipsa Ky | Wholesale & retail | 2008 |
| Koskenheimo Oy | Wholesale & retail | 1984 |
| Kostin Service Oy | Transport & logistics | 2011 |
| KotPytHam Oy | Information & communication | 2020 |
| Kotakari Oy | Real estate | 1990 |
| Kotekman Oy | Manufacturing | 1994 |
| Kotelnikoff Oy | Administrative & support | 2019 |
| Koti- ja Kiinteistöpalvelut Klingberg Oy | Administrative & support | 2020 |
| Koti- ja Terveyspalvelut M. Broas Ky | Health & social care | 2000 |
| Kotiapu Onnellinen avoin yhtiö | Health & social care | 2017 |
| Kotiapu Silmu Oy | Health & social care | 2025 |
| Kotijoukot A.S.A.P. Oy | Health & social care | 2012 |
| Kotipalvelu Anne Hoikkala Ky | Health & social care | 2006 |
| Kotipalvelu Järvi Oy | Health & social care | 2001 |
| Kotirannikko Oy | Real estate | 1997 |
| Kotka Beger Oy | Transport & logistics | 1985 |
| Kotka City Marina Oy | Wholesale & retail | 2024 |
| Kotka Coatings Oy | Construction | 1993 |
| Kotka Consplan Oy | Information & communication | 1989 |
| Kotka Elektroniikka kommandiittiyhtiö | | 1983 |
| Kotka Maretarium Oy | Arts & recreation | 2001 |
| Kotka Marine Oy | Manufacturing | 1983 |
| Kotka Mix Ky | Wholesale & retail | 1993 |
| Kotka Power Point Oy | Manufacturing | 1997 |
| Kotka Renewables Energy Platform Oy | Professional & scientific | 2023 |
| KotkaGas Oy | Energy | 2016 |
| KotkaTec Oy | Construction | 1995 |
| Kotkan Aitta Oy | Hospitality | 2024 |
| Kotkan As-Mi Oy | Manufacturing | 1990 |
| Kotkan Asennus ja Huolto Risto Tarvainen Ky | | 1983 |
| Kotkan Asennuspalvelu Oy | Manufacturing | 1985 |
| Kotkan Asunnot Oy | Real estate | 1959 |
| Kotkan Asuntopalvelu Oy | Real estate | 2011 |
| Kotkan Auto-ja Venehuolto Oy | Other services | 2019 |
| Kotkan Autohuolto Oy | Other services | 2016 |
| Kotkan Autolasi Oy | Other services | 2015 |
| Kotkan Automaalaus Oy | Other services | 2008 |
| Kotkan Automaalit ja Autonvaraosat T. Keränen Oy | Wholesale & retail | 2021 |
| Kotkan Automyynti Ky | Wholesale & retail | 2013 |
| Kotkan Blinker OY | Other services | 2024 |
| Kotkan Caaraklinikka Kalevi Niemi Oy | Other services | 1986 |
| Kotkan City-Kaihdin Oy | Construction | 2023 |
| Kotkan Eläintuhkaus Oy | Other services | 2022 |
| Kotkan Energia Oy | Energy | 2003 |
| Kotkan Energiaverkot Oy | Energy | 2015 |
| Kotkan Esteettinen Klinikka Oy | Other services | 2025 |
| Kotkan Futis Oy | Arts & recreation | 2001 |
| Kotkan Golf Oy | Arts & recreation | 1986 |
| Kotkan Hammaslaboratorio Oy | Manufacturing | 1982 |
| Kotkan Hautaus- ja Kukkapalvelu Oy | Other services | 2012 |
| Kotkan Helmi Oy | Hospitality | 2013 |
| Kotkan Ilmastointitekniikka Oy | Construction | 2019 |
| Kotkan Isännöintipalvelu Oy | Real estate | 2000 |
| Kotkan JH-Suunnittelu Ky | Professional & scientific | 1998 |
| Kotkan Jakart Oy | Wholesale & retail | 1997 |
| Kotkan Julkiset Kiinteistöt Oy | Real estate | 2014 |