Abstract: The effect of Kappa Casein (K-CN) gene polymorphism on milk yield (305 day yield) and some reproductive performance (number of service/conception, calving interval, open period and gestation period) was investigated using 237 Chinese Holstein cattle. The polymorphism of K-CN was detected by Polymerase Chain Reaction-Single Strand Conformation (PCR-SSCP) technique. The obtained results elucidated that K-CN genotypes did not affect (p>0.05) 305 day milk yield; cows with genotype TT produced slightly higher milk than those of TC and CC genotypes. However, the effect of K-CN genotypes on reproductive performance revealed that K-CN genotypes were not significant (p>0.05) for any traits.