Abstract: Objective 　To investigate the expression of Cks1 protein and its relationship with the expression of Skp2, p27 ^Kip1 and tumor aggressiveness. Methods 　Flow cytomet ry was used to detect the expression of the three proteins in 20 cases of normal gast ric tissue and 64 cases of primary gastric cancers. Results 　The expression of Cks1 and Skp2 in gastric cancers was higher than that in normal gast ric tissue (χ² = 22. 69, Ρ< 0. 05 ;χ² = 13. 42, Ρ< 0. 05 respectively) . While the expression of p27 ^Kip1 was lower than that in normal gastric tissue (χ² = 14. 83, P < 0. 05) . A significant inverse relation was observed between the expression of Cks1 or Skp2 and of p27 ^Kip1 ( r = - 0. 649, P < 0. 05 ; r = - 0. 732, P < 0. 05, respectively) . While there was no correlation between the expression of Cks1 and Skp2 ( P > 0. 05) . The expression of Cks1 was significantly associated with tumor differentiation. (χ2 = 5. 05, Ρ< 0. 05) . While it was not associated with depth of invasion, lymph node metasis and clinical stages ( P > 0. 05) . Conclusion Cks1 may play an important role in human gast ric tumorgenesis and it may be an essential accessory factor for Skp2 in protease-dependent dest ruction of p27 ^Kip1.