Cloning and sequencing of the eighth intron of porcine MX1 gene indicated that a G167A substitution which can be detected by restriction endonuclease HpaⅡ.This polymorphism was analyzed with PCR-RFLP among six foreign and Chinese pig breeds.The analysis results showed that frequencies of allele B in six pig breeds was 0.83,0.89,0.94,0.87,0.89,0.55 in Large White,Landrace,Tongcheng,Qingping,Exi black pig,Large White ×Meishan F2 progeny pigs respectively.Statistical analysis in 180 Large White ×Meishan F2 progeny pigs showed that the HpaⅡ polymorphism in the F2 population was significantly associated with dressing percentage,lean meat percentage,and loin eye height.Additive effects of dressing percentage,loin eye height were significant.Dominance effect of height and lean meat percentage was significant.