The present study was aimed to investigate the expression of tumor suppressor gene PTEN (phosphatase and tensin homolog deleted on chromosome ten) in mouse endometrium during early pregnancy and its possible role during blastocyst implantation. Real-time fluorescent quantitative PCR (FQ-PCR) and immunohistochemical techniques were applied to detect PTEN mRNA and protein expressions in endometrium in un-pregnant and pregnant mice on days 1, 3, 4, 5, 7 of pregnancy, respectively. In addition, PTEN antisense oligonucleotide was injected into the horns of uterus in pregnant mice on day 3 of pregnancy and its effects on blastocyst implantation was detected in vivo. The higher expressions of PTEN mRNA and protein were observed in pregnant mice compared with that in un-pregnant mice, with a steady increasing from day 1 to 7 and reaching the maximal level on day 5 of pregnancy. PTEN antisense oligonucleotide decreased the number of implanted blastocysts compared with saline. The results suggest that PTEN might associate with apoptosis of luminal epithelial and decidual cells, coordinating decidualization of endometrium and invasion of trophoblastic cells. Thus, PTEN may participate in the process of blastocyst implantation in mice.