This study was performed to investigate the effect of rosiglitazone, a new antidiabetic agent, on in vivo synthesis of bone collagen. The mice were divided into low-fat diet group (LF), high-fat diet group (HF), and high-fat diet with rosiglitazone (6.3 $mu extrm{g}$/kcal diet) group (HF-Rosi), The synthesis of bone collagen was measured by stable isotope-mass spectrometric technique using $^2$$H_2O$ as a tracer. The $^2$$H_2O$ labeling protocol consisted of an initial intraperitoneal injection of 99.9% $^2$$H_2O$, to achieve approximately 2.5% body water enrichment followed by administration of 4％ $^2$$H_2O$ in drinking water for 3 weeks. Although body weight gain and daily diet intake were not significantly different between groups, HF-Rosi had slightly higher body weight gain and daily diet intake than LF and HF. In addition, HF-Rosi showed significantly higher body fat content than LF and HF. Bone collagen synthesis was reduced in HF than LF and further decreased by the treatment of rosiglitazone. These results suggest rosiglitazone affect body fat content and bone turnover in mice.