To investigate the expression of BMPR1A in various tissues during different physiological periods (follicular and luteal phases) and in ewes of different fecundity (monotocous and polytocous),and to analyze the association of its polymorphism with litter size in Small Tail Han (STH) sheep,qPCR was used to detect the expression of BMPR1A in 14 tissues in STH sheep,meanwhile,Sequenom MassARRAYSNP assay was applied to genotype three single nucleotide polymorphism sites (SNPs) of BMPR1A gene in different sheep breeds,and then the association between the BMPR1A polymorphism and litter size in STH sheep was analyzed. The results showed that the expression of BMPR1A in hypothalamus and ovary of polytocous ewes was higher than that of monotocous ewes,but did not reach a significant level (P>0.05). From genotyping,the genotype and allele frequencies of g.41128335A>T and g.41127600C>T loci of BMPR1A were significantly different (P<0.05) between polytocous and monotocous sheep breeds. The χ2 test indicated that the three SNPs were under Hardy-Weinberg equilibrium (P>0.05) in most of the sheep breeds. Association analysis showed that three loci of BMPR1A gene had no significant association with the litter size of different groups of STH sheep (P>0.05),and the litter size of mutation was higher than that of wild for g.41128335A>T and g.41127598A>G loci. Therefore,we concluded that there may be a certain positive correlation between the expression of BMPR1A gene and litter size in STH sheep,but the three SNPs had no significant association with the litter size of STH sheep,which indicated they may not be the key loci that affect the expression or function of BMPR1A. 