Thermoplastic starch (TPS), an inexpensive, renewable, widely available and biodegradable biopolymer, has been promoted as a promising alternative to synthetic polymers based on fossil resources. However, it exhibits weak mechanical properties and high moisture uptake. Reinforcing fillers have been used to improve the properties of thermoplastic starch. This work studies the effects of Al2O3 particle size on dielectric, thermal, physical, mechanical and morphological properties of thermoplastic starch-TiO2-Al2O3 composites at the fixed TPS:TiO2:Al2O3 weight ratio 97:2:1. The Al2O3 particle sizes tested were 0.05 mu m, 1 mu m and 5 mu m. Dielectric, thermal, mechanical and morphological properties were determined. With increasing Al2O3 particle size, slight increases were observed in contact angle, hardness and thermal stability, while dielectric constant, dissipation factor and glass transition temperature decreased. However, the Al2O3 particle size did not significantly affect tensile properties. Scanning electron microscopy was used to investigate the morphology in the composites. In summary, the incorporation of TiO2 and Al2O3 in thermoplastic starch could extend its potential in flexible films, compost bags and packaging applications.