The polymorphism of Interleukin-8 (IL8) gene were investigated for 610 Chinese Holstein cows of 30 bull families from a dairy farm in Shanghai using Polymerase Chain Reaction-Single Strand Conformation Polymorphism (PCR-SSCP) technique with a mixed animal model to verify the effects of the polymorphisms on some milk productive performance, tested day milk yield, tested day fat percentage, tested day milk protein percentage, 305 d corrected milk yield, 305 d milk fat yield, 305 d milk protein yield, and somatic cell score (SCS). The aim was to explore the significant molecular marker in practical dairy production. Three genotypes were identified and the genotypic frequencies of KK, KA, and AA were 0.187, 0.451, and 0.362, respectively. The gene frequencies of K and A were 0.412 and 0.588. The results showed highly significant (P < 0.01) association of IL8 mutations with tested day milk yield, 305 d milk protein yield, 305 d corrected milk yield and 305 d milk fat yield, SCS and tested day milk protein percentage (P < 0.05). However, no association (P > 0.05) with tested day milk fat percentage was recorded. The cows with KK genotype had higher tested day milk yield, 305 d milk protein yield, 305 d corrected milk yield and 305 d milk fat yield than those with AA and KA genotypes (P < 0.01). The least square mean of SCS for KK was significantly lower than that with AA and KA genotypes (P < 0.01). AA genotype was significant lower in tested day milk protein percentage than KK and KA genotypes (P < 0.05). The IL8 gene genetic diversity has a great genetic effect on milk traits and mastitis resistance and could be a useful genetic marker for Chinese Holstein breeding.