Abstract: Objective To prepare iodine-131(131I) labeled biodegradable microspheres with chitosan and collagen for treating liver cancer. Methods Collagen-chitosan microspheres (CCMSs) were prepared with type-Ⅰ collagen and chitosan using emulsification-chemical cross-linking method. The size of the CCMSs were determined by electron microscope. 131I-CCMSs were achieved using Chloramine-T. The labelling rate of 131I was recorded. The stability of 131I-CCMSs in vitro were evaluated in PBS or human blood serum through 192 h incubation. The HepG2 model was established in nude mice 28 d after subcutaneous injection of 106 HepG2 cells. The model mice were sacrificed 7 d after injection of 131I-CCMSs, blank microspheres, or PBS (five mice in each group) into the HepG2 tumor xenografts. Samples of various organs were collected to determine the distribution of 131I-CCMSs. The curative effect of 131I-CCMSs on liver cancer was assessed by staining with HE for histological analyses. Results CCMSs were synthesized with a smooth and spherical shape and an average diameter of (5.1±1.2) μm. A radiolabeling rate of 86.10% was achieved. 131I radio-loading remained stable: 92.00% in saline and 83.00% in human serum after 192 h incubation. 131I was mainly concentrated in the subcutaneous tumor tissues. Potent curative effects of 131I-CCMSs on subcutaneous tumor tissues were demonstrated. Conclusion Biodegradable CCMSs were successfully prepared and radiolabeled. The 131I-CCMSs exhibited potential curative effects on liver cancer, with high stability in vitro and in vivo.