Angiogenesis is crucial to successful implantation and decidualization, however, as an important angiogenic growth factor, the effect of Ang‐2 in the process of implantation and decidualization is still unknown. This study is to investigate the differential expression of Ang‐2 in mouse uterus during early pregnancy and its regulation by steroid hormones using in situ hybridization and RT‐PCR. There is no detectable Ang‐2 mRNA signal on days 1–5 of pregnancy by in situ hybridization. On days 6–8, Ang‐2 mRNA is mainly expressed in the primary decidua of mesometrial side, and the expression gradually increases. By RT‐PCR, a significantly higher level of Ang‐2 expression is observed on day 8 of pregnancy, although Ang‐2 expression can be found through days 1–8. Similarly, Ang‐2 is highly expressed in decidualized cells under artificial decidualization. In the ovariectomized mouse uterus, Ang‐2 expression gradually increases after estrogen injection and with peak levels at 12 hr, while progesterone injection can cause a decline in uterine Ang‐2 mRNA level, which reaches a nadir at 12 hr. These results suggest that Ang‐2 may play a key role in the process of mouse decidualization. Estrogen can induce the expression of Ang‐2 while progesterone can inhibit its expression in the ovariectomized mouse uterus. Anat Rec, 2012. © 2011 Wiley Periodicals, Inc.