Kaj Ramsteijn started at the age of 10 in the Feyenoord youth academy coming over from DWO Zoetermeer. As a central defender he faced a lot of competition in the first squad of Feyenoord. Mid June 2010 he transferred to SBV Excelsior. He signed a 2-year contract that will keep him at SBV Excelsior until the summer of 2012. He made his professional début on September 22, 2010 in a match against WKE Emmen. His début in the starting 11 was on October 24, 2010 against Ajax. Ramsteijn made his first goal in a match against Willem II on November 27, 2010. The game ended in a 1-1 draw. After his first season at professional level, Ramsteijn was rewarded for his good season with a transfer to his former club Feyenoord, who has an extensive partnership agreement with Excelsior, together with team-mates Guyon Fernandez & Miquel Nelom.