A member of the Polish national junior team since 1965, Kazimierz Jasiński raced for Legia Warszawa, prior to returning to Radom and representing the colors of Radomiak and Broń. He had his best year in 1968, when he was a part of the Polish team that won the Peace Race (he placed 11th individually). He was also selected to race in the Olympic road race (59th) after winning the Polish national championships. Earlier, Jasiński had won two Polish titles in the road team time trial, but he was not picked to race in that event at the Olympics. Other notable victories were a stage win in the 1969 Milk Race and the 1967 Baltic Sea Friendship Race. After his active career, Jasiński worked as a club coach, also briefly in the US.