The diffusion coefficients, D12, of the ten binary mixtures of the noble gases: He, Ne, Ar, Kr and Xe, have been measured as a function of temperature and concentration using a method similar to the one described in ref. 1. In general the diffusion coefficients are well described by the Chapman-Enskog theory with the Lennard-Jones (12−6) potential or the (exp-6) potential. From the experimental data the potential parameters, εij and σij, of the mixed interaction have been calculated. Some combination rules connecting the mixed parameters with those of the pure components have been tested. Only the rule εijσ6ij = (εiiσ6iiεjjσ6jj)12 agrees with the experim ents.