The chitosan with different molecular weights (MW: 50 kDa, 250 kDa, 500 kDa and 1 000 kDa) were used to respectively combine whey proteins to form their composite films. It was expected that chitosan/whey proteins films endowed with versatile functionalities to meet practical requirement of food packaging applications. The equal volume of 3% (m/V) chitosan dissolved in 2% (m/V) acetic acid solutions and 12% (m/V) preheated (80 ℃ for 30 min) whey protein solutions was used to prepare resulting film-forming solutions after 2.4% (based on whey protein content, m/m) glycerol to make cast composite films. The functional propertied of the prepared composite films were characterized by their thickness, puncture strength, light transmittance and transparency, and swelling properties (in various solutions, e.g.: distilled water and acids). The result shows the size of chitosan molecular weight remarkably increased the resulting film’s thickness, but reduced puncture strength, and meanwhile lowered the light transmittance and transparency, whereas effectively prevented ultraviolet light from penetrating. Overall, these variations in the film functionalities were attributed to chitosan dispersity when making cast films and confirmed by the morphological analysis.