Due to environmental concerns, biodegradable materials, which are currently used in many medical applications, are being considered as a candidate for replace plastics in the future. One of the most common mass production processes to shape biodegradable materials is injection molding. However, the material manufacturers usually do not provide optimized parameter information. In this research, two biodegradable materials, PLA 3001D and Biomax, are investigated. Experiments are conducted utilizing the Taguchi method to determine optimal injection molding parameters, which include injection speed, injection pressure, holding pressure, and cooling time. Shrinkage was the major index to evaluate the injection results. As a result, the best combinations of parameters were determined.