To investigate the genetic diversity of six Chinese indigenous pig breeds in Shandong province (Laiwu Black, Dapulian Black, Licha Black, Yantai Black, Yimeng Black and Wulian Black), explain their genetic relationship and assess their integrity and degree of admixture with three Western commercial breeds (Landrace, Yorkshire and Duroc), 303 individuals from these breeds were genotyped for 26 microsatellite markers. In general, high genetic diversity (observed heterozygosity ranging from 0.5495 to 0.7746) and large breed differentiation ($F_{ST}$ = 0.188) were observed. The indigenous pig breeds in Shandong exhibited consistently higher levels of genetic diversity than the three Western breeds. However, compared with the Western breeds, which have an $F_{ST}$ value of 0.252, the indigenous breeds in Shandong have smaller $F_{ST}$ value of 0.145. The analysis of breed relationship indicated that the six indigenous breeds are classified into two groups. One includes four breeds, Licha, Yantai, Yimeng and Wulian, which have experienced large gene introgression of the Western breeds through progressive crossbreeding as well as gene flow among themselves. The other includes Laiwu and Dapulian, which are less influenced by the Western breeds and other indigenous breeds in Shandong in the recent past. The results show that some measures must be taken to effectively protect these indigenous pig breeds in Shandong.