The purpose of this study was to investigate the effects of sea tangle (ST) extracts on formation of collagen and collagen cross-link in ovariectomized rats. From day 3 until 42 after the ovariectomy, Sprague-Dawley female rats were randomly assigned to the following groups: sham-operated rats(Sham), ovariectomized control rats (OVX-control), ovariectomized rats supplemented with ST at 50 mg/kg bw/day (OVX-ST50), 200 mg/kg bw/day (OVX-ST200). The ethanol extraxcr of ST was orally administrated at 1 ml/day. The change of collagen content was investigated in bone, cartilage and skin of ovariectomized rats. Effects of ST extract on the amount of collagen was examined by measuring the hydroxyproline, which is a specific amino acid existing in collagen. The ovariectomy resulted in a decrease in the levels of collagen content in bone and cartilage tissues. However, the supplementation with the sea tangle extract prevented the decrease in the collagen level in bone and cartilage tissues. Pyridinoline is pyridinium cross-link formed in the mature form of collagen from lysine and hydroxylysine residues. Although the pyridinoline content in bone collagen declined after ovariectomy, it was recovered to a normal level of Sham group by the supplementation with the ST extracts. In addition, the deoxypyridinoline content in bone collagen, which was reduced after ovariectomy was enhanced to normal level by the supplementation with the ST extract. These results was consistent with the conclusions based on estrogenic activities of ST.