The drainage characteristics and surface lateral diffusion properties of thin liquid films (foam lamellae) formed by BSA (bovine serum albumin) and Tween 20 were studied using optical microscopy including epi-illumination and fluorescence recovery after photobleaching. The concentrations of the surfactant and protein at the aqueous phase interface, the composition of the interface (BSA, Tween 20, and BSA-Tween 20 mixtures), and the aqueous phase composition (1 M ethanol and 0.5 M sucrose) were the variables studied. This study has revealed many complicated effects arising from film-film and film-subphase interactions as a function of the variables studied. The interactions between Tween 20 and BSA at the interface were found to dependent not only on the interfacial composition but also on the subphase composition.