Objective To observe the sequential changes of collagen fibers in rats with diethylnitrosamine (DEN)-induced hepatocellular carcinoma (HCC), so as to provide a reference for pathogenesis research of HCC. Methods Fifty male Wistar rats, weighing 100-120 g, were randomly divided into normal group and HCC model group. The model group was intraperitoneally administered with 50 mg/kg DEN (0.1 mL), twice a week for 4 weeks, then once a week for another 10 weeks. The control group was given normal saline (0.1 mL) in the same manner. Finally the rats were sacrificed; the normal and diseased liver tissues were observed by H-E, Masson and argyrophilic fiber staining. The expression of collagen type Ⅰ and type Ⅲ mRNA was detected by fluorogenic quantitative PCR; the expression of matrix metalloproteinase (MMP) was examined by gelatinases spectrometry. Results Cirrhosis was found in rats 5 weeks after treatment with DEN and HCC was induced 14 weeks after DEN treatment; collagen deposition in liver tissues increased in a progressive manner, and the collagen contents in the HCC tissues was greatly less than that in the adjacent tissues, showing a decreasing trend. The contents of MMP-2 and MMP-9 in the HCC and adjacent tissues had opposite changes compared with collagen. Conclusion Collagen deposition in cirrhosis liver tissue is increased during the process of DEN-induced HCC, but it is decreased in HCC tissues in a progressive manner, which indicates that collagen might be degraded during the progression from cirrhosis to HCC.