The nm23 gene family was involved in cellular multiphysiopathological processes including differentiation, development, apoptosis and cancer promotion, progression or metastasis. Some data indicate that nm23 plays an important role in regulating reproductive processes. In the present study, we analyzed the proteome of the implantation sites and the peri-implantation sites in NIH. mice on Day 5 of gestation by using two-Dimensional gel electrophoresis (2-D PAGE), while the virgin mice as the control. A protein spot with pI 7.1, Mr 18 kDa showed up-regulated expression in endometrium during the blastocysts adhesiveness. Using matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS), this protein was identified as nm23-M2/NDPK B. The nm23-M2 expression in mice endometrium was shown progressive increase on Day 5 of gestation by RT-PCR, which was consistent with the result obtained by immunohistochemistry. These findings suggest that nm23-M2/NDPK B was involved in the process of blastocyst implantation.