In this paper, a method of determining the percentage of type Ⅱ collagen in extracellular matrix of cultured chondrocytes or caritilage tissue in terms of the spectrophotometric densities of specific cyangen bromide peptide bonds on SDS-polyacrylamide gels has been used. The results show that the free radical generating systems, including Fe(Ⅱ)-EDTA,Xanthine Oxidase-Xanthine. Fulvic acid and Fusarium toxin, can cause chondrocytes to synthesize and secrete mainly type Ⅰ collagen instead of the normal type Ⅱ collagen. In addition, The collagen type change can be inhibited by Se(Ⅳ) compounds.