Retinol binding protein 4 (RBP4), an important candidate gene for traits of sow litter size (LS), plays a key role in vitamin transportation on the maternal-fetal interface during swine pregnancy. Candidates of exonic single nucleotide polymorphisms (SNPs) in gene RBP4 were scanned through bioinformatics analysis, and SNP A1027G , neighboring to MspⅠRFLP (SNP G1223C) with molecular marked was validated, and the correlation between LS traits and polymorphisms of RBP4 gene were further analyzed both on the population of Large White and Hunan black. Results exhibited that both RBP4 MspⅠ RFLP and the lately reported SNP A1027G were significantly correlated with swine LS traits (P<0.05). The average LS traits performance of most of advantage RBP4 haplotypes was better than those of advantage genotypes with single locus on SNPs. It was suggested that the haplotype of RBP4 gene was a more efficient molecular marker for the improvement of swine LS traits than SNP with a single locus.