By comparing the manufacturing of conventional plastic with biodegradable plastic, a brief investigation of plastic and future developing trend was done. It is essential to investigate a biodegradable polymer which is produced with low cost and recyclable resources. An experiment was carried with cornstarch and kappa-carrageenan, which aim to produce a natural polymer can be biodegradable and has similar properties to conventional plastic. This experiment focuses on the mechanical properties and solubility of different amount ratio of the dry components to find out whether it has any functions that can be use in daily life. The results show the membrane with higher ratio carrageenan represents lower solubility, better mechanical properties and water resistance, but these properties become weaker in dry environment. The results provide a theoretical basis of the application of this polymer in medical region and food packaging.