This study was aimed to investigate whether and how prenatal caffeine exposure (PCE) could induce osteopenia in the adult offspring. Pregnant rats were treated with prenatal caffeine 12 mg/100 g body weight per day from pregnant day 9 to 20, while rat bone marrow mesenchymal stem cells (BMSCs) were treated with exogenous corticosterone during osteogenic induction. Shorter femur and primary ossification center was observed in the PCE offspring, as well as less bone trabecular and poor biomechanical intensity. Local gene expression of glucocorticoid receptor (GR) and angiotensin converting enzyme (ACE), as well as angiotensin 2 content, was found to be stimulated, while the expression of bone gamma-carboxyglutamate protein (BGLAP), alkaline phosphatase (ALP) and bone sialoprotein (BSP) was found to be suppressed, with hypomethylation of ACE promoter. Corticosterone (1250 nM) suppressed osteogenic differentiation of BMSCs and gene expression of BGLAP, ALP and BSP, which was attenuated by enalapril, while it stimulated ACE mRNA expression and induced hypomethylation of ACE promoter, which was attenuated by mifepristone. It indicated that PCE caused bone growth retardation and adult osteopenia in offspring, which might be triggered by the activation of local RAS induced by excessive maternal glucocorticoid, while the hypomethylation of ACE gene might be the key point of the sustained activation of the local RAS.