The purpose of this study was to investigate the effects of Porphyra tenera (PT) extracts on formation of 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 PT at 50 mg/kg bw/day (OVX-PT5O), 200 mg/kgbw/day (OVX-PT200). The PT ethanol extracts were orally administrated 1 mL per day. Body weight gain, food intake and food efficiency ratio were significantly different among the groups. The change of collagen content was studied in lung, bone, cartilage and skin of ovariectomized rats. The effects of PT extracts on the amount of collagen were examined by measuring the hydroxyproline, which is a specific amino acid existing in collagen. Pyridinoline is pyridinium cross-link formed in the mature form of collagen from lysine and hydroxylysine residues. Pyridinoline content was analyzed by HPLC. Pyridinoline content in bone collagen was decreased by ovariectomy but supplementation with the PT extracts was similarly increased to Sham. These results suggest that the PT supplementation could decrease bone loss in postmenopausal women.