As pyridinoline is one of the predominant cross-lins in a mature collagen, pyridinoline formation may be an essential step during the growth process to obtain normal mechanical strength in collagen fibrils. However, the excess formation of pyridinoline in collagen will probably make the tissue stiffer, less soluble and less digestible by enzymes. We investigated the changes of pyridinoline of bone collagen and the role of ascforbic acid(AsA) on the formation of pyridinoline. The pyridinoline content of bone collagen significantly increased during incubation for 1~5 weeks at 37$^{circ}C$ in vitro. The addition of AsA decreased pyridinoline to half the amount found in controls with 5 week incubation. When dehydroascorbic acid(DHA) and L-2, 3-diketogulonic acid (DKG), the oxidative products of AsA, were supplemented to bone collagen solution instead of AsA, the content of pyridinoline in bone collagen was about 80% or 70% that of controls, respectively. These results suggest that pyridinoline content decreases by the addition of AsA in vitro. Furthermore, it was shown that AsA in oxidized from also affected the formation of pyridinoline.