The effect of sodium caseinate addition on corn starch films was studied in terms of microstructural, mechanical, optical and water and oxygen barrier properties and the changes they underwent during their 5 weeks' storage under controlled conditions. The influence of the polymer mixture on the degree of crystallization of the films was also analysed. The following starch: protein ratios were considered. 100:0, 75:50, 50:50 and 0:100. SEM Microstructure analysis revealed the compatibility of both hydrocolloids since no phase separation was observed. The addition of sodium caseinate to the starch films provided films that were less stiff and resistant to fracture but more flexible and deformable than pure starch films, with similar water vapour permeability values. The films became more permeable to oxygen as their sodium caseinate content increased in line with the higher permeability values of the protein film. Incorporating sodium caseinate to starch films provoked a slight increase in transparency, but a loss of gloss, which also decreased in composite films during storage. The re-arrangement of polymer chains during storage caused a loss of mechanical resistance, stretchability and gloss in composite films. ; Spanish Ministerio de Economia y Competitividad AGL2010-20694 ; Jiménez Marco, A.; Fabra Rovira, MJ.; Talens Oliag, P.; Chiralt Boix, MA. (2012). Effect of sodium caseinate on properties and ageing behaviour of corn starch based films. Food Hydrocolloids. 29(2):265-271. doi:10.1016/j.foodhyd.2012.03.014. ; Senia ; 265 ; 271 ; 29 ; 2