In this work, a biodegradable composite made from corn starch and microcrystalline cellulose (MCC) is prepared using solution‐casting method. This work provides a highly‐efficient and easily industrialized method for the fabrication of high‐performance starch composite reinforced with MCC. Prior to composite fabrication, the simultaneous exfoliation and alkali treatment is achieved through the synergetic effect of mechanical and chemical actions generated from ball milling in the presence of sodium hydroxide. The tensile strength of starch/MCC composite containing only 2 wt% MCC is increased by 49% compared with that of neat starch. In addition, the starch/MCC films exhibit excellent mechanical properties at different relative humidities. This work could significantly expand the application of starch and cellulose, thus reducing the need for petroleum‐based plastics.