Quercetin is a widely distributed bioflavonoid which inhibits the growth of tumour cells. The present study was designed to investigate quercetin- cyclodextrin inclusion complex for in vivo growth inhibition of murine tumours. The LD10 of inclusion complex was found to be 50mg/kg. At this dose no evidence of tumour growth inhibition was observed. However, the preparation offered significant protection against radiation induced myelosuppression in mice and the results suggest that – the addition of flavonoid will improve the effectiveness of radiation therapy for the treatment of cancer.