Many polymers have been used to develop biodegradable films but starch is an attractive material for this purpose because it is an abundant renewable and low cost material. In this study, the effect of glycerol (GE) as a plasticizer on the physical properties of carboxylated styrene-butadiene rubber/cassava starch blend films was investigated. The results show that the addition of GE reduced the brittleness of the films and promoted their flexibility. The films also exhibited higher water absorption ability, higher moisture contents, and better elongation at break with increasing concentrations of GE because the GE reduced the interaction strength between the polymer chains, leading to improved mobility. Furthermore, films containing GE easily hold water in their matrix because the active hydroxyl groups in the GE have a strong affinity with water molecules. This study demonstrated that a significant concentration of GE improved the films’ properties and these inexpensive biodegradable films have promising applications as alternative packaging materials.