We investigated changes in serum undercarboxylated osteocalcin (ucOC) concentrations, bone turnover markers and spine bone mineral density (BMD) in women who had undergone bilateral oophorectomy during the premenopausal period. The study population comprised 141 bilaterally oophorectomized and 32 premenopausal women for a cross-sectional study. The longitudinal study consisted of 21 bilaterally oophorectomized women. Serum ucOC concentration, serum concentrations of intact osteocalcin (OC) and bone-specific alkaline phosphatase (BAP) as bone formation markers, urine N-telopeptide (NTx) concentration as a bone resorption marker and serum parathyroid hormone (PTH) concentration were measured. Serum concentration of ucOC in women at 1 month after bilateral oophorectomy was significantly (p<0.05) higher than that in premenopausal women and the high level was sustained after surgical menopause. On the other hand, serum OC concentration at 1 month after surgical menopause was not different from that in premenopausal women. In the longitudinal study, serum ucOC concentration at 1 month after surgical menopause was significantly (p<0.05) increased compared to that before bilateral oophorectomy, while serum OC concentrations before and at 1 month after surgical menopause were not significantly different. The results of this study showed that serum ucOC concentration rapidly increases in women after bilateral oophorectomy and that change in serum ucOC concentration after surgical menopause is different from change in serum OC concentration.