Abstract: The aim of this study was to evaluate the conserved effect for Mashen pig by analyzing the trend of genetic diversity of Mashen pig populations during 1999 to 2007 and to make the effective measures for conservation. A total of 21 microsatellite markers recommended by FAO-ISAG were used to study the genetic diversity and the changing trend of Mashen pig. The results showed that there were 105 alleles detected in the overall Mashen pig population. The mean allele number per locus and mean effective allele number were 5 and 2.244 0, respectively. The mean observed heterozygosity and the mean PIC were 0.317 6 and 0.391 9, respectively. From 1999 to 2007, the mean allele number per locus, mean effective allele number, mean observed heterozygosity and the mean PIC of Mashen pig population declined from 4.285 7 to 3.428 6, 2.509 5 to 1.977 0, 0.311 6 to 0.298 1 and from 0.441 to 0.341, respectively. The results indicated that the homozygosity of Mashen pig was high and not polluted by other pig breeds, but the genetic diversity was becoming lower. The real-time monitoring on the change of genetic diversity of Mashen pig is needed in the future conversation and usage of Mashen pig. We should pay more attention to some alleles with low frequency to avoid them lost during generation passage.