The purpose of this study was to investigate the effect of sizes of turmeric microparticles (as a reinforcing agent) on the mechanical and biodegradation properties of cornstarch-based bioplastic material. The following fabrication procedures were performed: (1) diluting cornstarch in water; (2) making homogeneous mixture of cornstarch, glycerol and acetic acid by heating at less than 100ºC, (3) additional turmeric with a specific size (i.e. 250, 125, 100, 74 μm); (4) molding process; and (5) drying process to obtain solid bioplastic materials. This study shows the importance of reinforcing agent size for improving the mechanical properties of bioplastic materials. The smaller turmeric size brings better mechanical properties than the larger turmeric size that has more void space. To support the analysis, the present study also was completed with a literature review regarding bioplastic production and proposal bioplastics material crack phenomena during mechanical testing.