Eighty-one haplotypes were obtained from the complete Cytochrome b gene (Cyt b) of 99 Laxmann’s shrew Sorex caecutiens collected from three populations (Daxing’anling, Xiaoxing’anling and Changbaishan Mountains) in Northeast China. There was high overall genetic diversity (0.9940) and no significant variation in the genetic diversity of these three populations. Analysis of molecular variance showed that the differentiation among the three populations accounted for only 2.48% of total variation, that between sampling locations accounted for 0.34% of total variation, and that variation within sampling locations accounted for 97.19% of total variation. Genetic differentiation was not correlated with geographical distance separating populations. The phylogenetic tree was constructed based on the Cyt b of S. caecutiens and on data downloaded from GenBank. The phylogenetic tree branched into three lineages. S. caecutiens from Japan's Hokkaido formed a small lineage.  S. caecutiens from Jeju Island, Republic of Korea, formed another small lineage. S. caecutiens from Northeast China and other regions of Eurasia formed a large lineage. There was no further obvious differentiation of the genetic structure on the Eurasian mainland. Median-joining network analysis showed results similar to the phylogenetic trees, which suggested there was no obvious genetic differentiation in S. caecutiens from the Eurasian continent lineages excepting the lineages from Hokkaido in Japan and Jeju Island in Republic of Korea. The correlation was weak between genetic

differentiation and geographical distance. The analysis of population history showed that S. caecutiens in northeast China had experienced population expansion.