Due to several important limitations for applications of thermoplastic starch (TPS), thermoplastic acetylated cassava starch (TPACS) polymer was reinforced by different contents of neem wood sawdust (SD). Thermoplastic cassava starch (TPCS)/SD composites were also prepared and reinforced by different SD contents and compared with the TPACS/SD composites. Morphological, thermal, and biodegradable properties of different composites were also examined. The results showed that IR absorption bands of OH stretching and OH bending vibrations shifted to lower wavenumbers, indicating new hydrogen bond formation for all composites. Stress at maximum load and Young's modulus were significantly improved when the SD content increased for all the TPACS/SD and TPCS/SD composites; strain at maximum load was higher for the TPACS/SD composites. A decrease in water uptake was detected when the SD reinforcement was incorporated into either the TPACS or TPCS matrix.