Randomly 50% deacetylated chitin, called Chi, was examined on the biodegradability, body distribution and urinary excretion after the intraperitoneal (ip) administration to mice. These characteristics were investigated using fluorescein isothiocyanate (FITC)-labeled Chi (FTC-Chi). The in vitro biodegradability was investigated by incubation with lysozyme and murine plasma and urine. The degradation of Chi or FTC-Chi was accelerated by lysozyme, plasma and urine. The molecular weight was checked by gel-chromatography. The degradation product showed a fairly small molecular weight and contained no FTC-Chi of a large one. The body distribution and urinary excretion of FTC-Chi were investigated at 1, 14 and 24 h after the ip injection to mice. FTC-Chi moved fast to the kidney and urine, and was scarcely distributed to the liver, spleen, abdominal dropsy and plasma. Most of FTC-Chi was excreted into urine after 14 h, and the molecular weight of the excreted FTC-Chi was as small as that of the product obtained by the long in vitro incubation. Therefore, Chi is considered to be highly biodegradable and easily excreted in urine, and further it is suggested to have no problem on accumulation in the body; however, at the same time, Chi is found not to operate as a polymer support showing long retention in the body.