The work investigates the role of non-ideality in interracial multicomponent mass transfer with chemical reaction. These effects are produoed by two different mechanisms. First non-ideal thermodynamics must he considered for the mixture, since it may affect both the diffusion rate (the true driving force for diffusion being the chemical potential gradient) and the reaction rate. On the other hand, the diffusion coefficients may vary with composition, due to the intrinsic kinetics of diffusion. These phenomena have been investigated for two limiting cases of fast reactions, that is, pseudo first order and instantaneous reaction. Diffusion rate was modelled by means of the generalized Maxwell-Stefan equation and the reaction was supposed bimolecular. The composition dependence of the diffusion coefficients plays a significant role only when the Maxwell-Stefan diffusivities at infinite dilution differ considerably from each other (four or five times), thus excluding most systems. Relevant actions caused by non-idea1 thermodynamics have been detected only in highly non-ideal systems. Therefore, the expressions developed for ideal systems can often be extended to non-ideal ones.