Plastic synthetic is widely used in various purposes, ranging from household to industrial purposes. However, in spite of its superior, conventional plastic has several weaknesses, which the plastic waste can pollute the environment. It is important reason for replacing the use of conventional plastic with degradable plastics. Biodegradable plastic is a plastic that can be decomposed naturally by bacteria. The biodegradable plastic can be made from agricultural products such as cellulose and starch. Biodegradable plastic in this report was made from starch of purple taro tuber (Xanthosoma sagittifolium) and chitosan. The materials was perform using variables i.e. temperature, times and ratio of chitosan and starch. The mechanical and physical properties of biodegradable plastic were investigated by tensile strength testing, plastic degradation test by soaking in EM4 (Effective Microorganism) solution, and Fourier Transform Infra-Red (FTIR) was used to identify the chemical structure in biodegradable plastics. The specimens of the research were made by using starch of purple taro tuber with a weight of 10 g, 100 ml of 0.5% acetic acid, 2.5 ml of glycerin, a ratio of starch and chitosan of 0.075, with a temperature of 80 ºC, stirring speed of 300 rpm and a processing time of 75 minute. The result of the research showed a tensile strength of 2.32 MPa with elongation of 44.62%. The biodegradable plastic from the starch of purple taro tuber and chitosan can be degraded with the of EM4 solution until of 35 days. The investigated by using FTIR showed chemical structures of OH phenolic alcohols, C=O carbonyls, and CO esters, that can be easy decomposed. Thus, the plastic from the starch of purple taro tuber is environmentally friendly plastic.