The hydrogen-deuterium exchange reaction was performed for hydrogenation of D-5-1-pentene (4,4,5,5,5) under realistic cobalt Fischer-Tropsch synthesis conditions. In the presence of CO, the added deutero-1-pentene did not show any significant H/D exchange but a step-wise H/D exchange occurs when CO was replaced with N-2. The inhibition effects of CO and other FT products on H/D exchange of D-5-1-pentene and a pressure dependency effect on H/D exchange are observed.