In this article we provide results on the preparation of starch-based block copolymer with polyacrylic acid by radical polymerization. Starch was pregelatinized and then reacted with acrylic acid in the presence of radical polymerization initiator. Resulting mixture was used to prepare cast-films. Structure of the polymer films was investigated by gel filtration chromatography, FTIR and DCS analysis. It was found that structure of the films represents starch-graft-polyacrylic acid dispersed in a starch matrix. Results of DCS and FTIR suggested that polyacrylic acid acts as additional plasticizer for starch films.