Objective: The objective of this study was to evaluate the role of Activin A and p38 beta MAPK-activated signaling in human leiomyoma cells, myometrial cells and mouse myometrial tissues. Methods: The immortalization human leiomyoma cells (HuLM), the immortalized human myometrial cells (HM) and mouse myometrial tissues were treated with Activin A (4 nM) and/or specific p38 inhibitor SB202190 (10 mu M) for different days of interval (to measure proliferation rate) or 1 h (to measure signaling molecules) or 48 h (to measure proliferating markers Ki-67, ECM mRNA, and/or ECM protein expression) by real-time PCR, Western blot, and/or immunocytochemistry. Results: Activin A induced cell proliferation and ECM proteins accumulation in HuLM cells via p38 MAPK. Activin A also induced myofibroblastic transformation in HM cells and mouse myometrical tissues via the phosphorylation of p38. The effects of Activin A in leiomyoma cells, myometrical cells and tissues were abolished by p38 alpha/beta MAPK inhibitor SB202190. Conclusion: This study demonstrates Activin A-p38 MAPK signaling pathway in leiomyoma and myometrium may contribute to excessive ECM production, leiomyoma growth and progression. Targeting Activin A-p38 MAPK signaling pathway could be a potential therapeutic intervention for uterine leiomyoma. Published by Elsevier Inc.