To gain an insight into intracellular mechanisms involved in differentiation of human endometrial cells into decidual cells, we examined the presence of Akt, an emerging intracellular mediator in human endometrial stromal cells (ESC). We explored the mechanisms regulating Akt phosphorylation during the process of progesterone‐induced decidualization using a primary cell culture system of ESC. Both Akt and phosphorylated Akt (phospho‐Akt) were present in ESC. The total Akt level in ESC cultured for 12 days in the absence of ovarian hormones was similar to ESC treated with estradiol (E₂) at 10 ng/ml, progesterone at 100 ng/ml or E₂ plus progesterone (E₂ progesterone), whereas the levels of phospho‐Akt were markedly decreased with progesterone or E₂ progesterone, compared to control cells. Notably, phospho‐Akt levels increased during 12 days of culture in parallel with an increase in total Akt in untreated cells. An increase of phospho‐Akt in the E₂ progesterone‐treated cells was marginal. The level of phospho‐Akt in E₂ progesterone‐treated cells was markedly reduced compared to control cells at all time points examined. Treatment of the cells with 8‐bromo‐cAMP decreased the amount of phospho‐Akt in ESC in as short a period as 15 min, while no discernible change was observed in the untreated cells. Conversely, H89, an inhibitor of protein kinase A (PKA), significantly increased the amount of phospho‐Akt. The addition of H‐89 reversed the decrease in the level of phospho‐Akt seen in the cells treated with E₂ progesterone. Thus, we demonstrated the presence of Akt and its phosphorylated form in human ESC. We further suggest that Akt phosphorylation through the cAMP/PKA signal transduction pathway may regulate cellular functions coupled with decidualization.