The aim of the present study was to elucidate the effect of the water soluble chitosans on the removal of contaminated radiostrontium (Sr-85) from the bone of mice. The remaining radioactivities in intravenously injected controls(group 1) were higher than in intraperitoneally injected controls (group 4, P<0.01). The % retention at day 5 were $57.7{pm}1.9%,;54.4{pm}1.2%$, respectively. Single intravenous injection of 0.3% water soluble chitosan and continuous oral ingestion of 10% water soluble chitosan for 15 days were' ineffective on the removal of contaminated radiostrontiums. Multiple intravenous or intraperitoneal injections of water soluble chitosan effectively removed contaminated radiostrontiums(P<0.01 vs controls). In conclusion, water soluble chitosan might remove once incorporated radiostrontium from bones of mice. Further studies were needed to elucidate the mechanism of the removal.