Childhood obesity is a metabolic disease characterized by accumulation of excessive fat. Bisphenol A (BPA), a potential obesogen compound, possesses an estrogen mimetic activity and endocrine disruption effect. MicroRNA-21a-5p (miR-21a-5p) is reported to regulate the adipogenic differentiation. Our study showed that miR-21a-5p overexpression significantly decreased the red lipid droplets and triglyceride level in BPA-induced 3T3-L1 cells. BPA induced the mRNA and protein expression levels of PPARy, C/EBPa and adiponectin, and the induction was inhibited by miR-21a-5p mimics transfection. MiR-21a-5p mimics inhibited the GR activity, GR phosphorylation (S220, 521a-5p2, and S234), and the activation of p38/MAPK pathway, which are elevated by BPA treatment in 3T3 -L1 cells. MiR-21a-5p overexpression inhibited the protein level of MKK3, but not in the mRNA level. Luciferase activity assay showed that miR-21a-5p directly targeted map2k3 3'-UTR. MKK3 overexpression attenuated the effect of miR-21a-5p mimics transfection on 3T3 -L1 differentiation. We also assessed the body weight, fat mass and the content of serum lipid in rats subcutaneous injected with BPA and miR-21a-5p mimics. MiR-21a-5p overexpression attenuated BPA-induced obesity in vivo. These findings suggested that miR-21a-5p inhibited BPA induced adipocyte differentiation by targeting map2k3 through MKK3/p38/MAPK in 3T3-L1 cells, providing a potential therapeutic strategy for BPA induced obesity. (C) 2016 Elsevier Inc. All rights reserved.