This study aimed to develop bioplastic from a combination of tapioca starch and casein, as well as to determine the physical characteristics, such as thickness, density, light transmittance, and opacity. The composition of the bioplastic was made from two types of casein, namely commercial casein and rejected milk casein, with a ratio of tapioca starch and casein consisting of 4 treatment groups (4:0, 3:1, 2.5:1.5, 2:2). Each treatment was repeated 6 times. The physical characteristics data obtained were analyzed using a two-way ANOVA completely randomized design variance analysis. If there is a difference, it is continued with the Duncan multiple range test (DMRT). The results showed that the ratio of starch and casein had a very significant effect on all test parameters (P<0.01). An increase in commercial casein (CC) and rejected milk casein (EMC) increased thickness and opacity, while density and light transmittance decreased. Based on the research, bioplastic can be made with a combination of different ratios of tapioca starch and casein types with the best result were at a ratio of 2:2 which produced a thickness of 0.29 mm, light transmittance of 20.03%, opacity of 2.51%, while the density had the smallest value at 0.15 gr/cm 3 . In conclusion, rejected milk casein could be used as biomaterial to make bioplastic combined with tapioca starch.