Litter size is one of the most important economic traits for pig production as it is directly related to production efficiency. To evaluate the effects of the adiponectin (ADIPOQ) gene on porcine litter size, we investigated ADIPOQ polymorphisms in three breeds, Wannan Black pigs, Berkshire pigs, and BW pigs (crossbred pigs produced from mating male Berkshire pigs and female Wannan Black pigs), using the PCR-SSCP method. Three SNPs (c. 178G > A, c. 1165A > G, and c. 1138G > A) were identified. In Wannan Black pigs, association analysis indicated that the c. 178G > A SNP genotype was significantly associated with an effect on total number born (TNB; P < 0.05) and the number born alive (NBA; P < 0.05) in primiparity. The c.1138G > A SNP was significantly associated with an effect on TNB (P < 0.05) and NBA (P < 0.05) in primiparity and multiparity. In addition, three of the nine possible genotype combinations, AACC, AACD, and AGCD, were found. AGCD resulted in primiparous and multiparous sows with the highest TNB. These results indicated that polymorphisms in the ADIPOQ gene could be used for marker-assisted selection programs for the genetic improvement of reproductive characteristics in pigs.