The effects of a Lactobacillus casei 393 fermented milk product (FMP) on bone metabolism were examined. FMP (>0.1 mg mL(-1)) supplementation significantly increased osteoblastic MC3T3-E1 cells proliferation whereas skim milk powder supplementation did not show any positive effect up to 1 mg mL(-1). The FMP (1%) supplemented ovariectomised rats had increased bone weight, bone mineral density, and bone breaking force compared with control ovariectomised rat. In addition, the activity of tartrate resistant acid phosphatase, a biomarker of osteoclasts, was significantly reduced in the FMP group. Based on the results, the L casei 393 FMP had a preventative effect on bone loss in ovariectomised rats. (C) 2009 Elsevier Ltd. All rights reserved.