This work represents the functionalization of nanoscale biodegradable polymer and controls its sustained release rate for long time period. The polymer was synthesized by free radical polymerization reaction. Starch cellulose acetate co‐acrylate (SCAA) polymer was prepared and loaded with doxorubicin drug. The polymer before and after loading was characterized by Fourier‐transform infrared spectroscopy, gel permeation chromatography, and high‐resolution transmission electron microscopy. The release‐rate study illustrated good property through sustained release and extended to ∼65 days. The antiproliferative effect of doxorubicin slowly released from the prepared nanobiodegradable polymer illustrated growth inhibition potency toward human colon and liver cancer cell lines LoVo and HEPG2. POLYM. COMPOS., 38:E34–E41, 2017. © 2015 Society of Plastics Engineers