The effect of a bicomponent beta-nucleator on the non-isothermal and isothermal crystallization of ethylene/propylene random and block copolymers, containing small amounts of ethylene and having nearly the same molecular weights, was studied using differential scanning calorimetry (DSC). The results obtained indicated that the beta-nucleator is effective in inducing the beta-form and in reducing undercooling in both copolymers. However, it is more effective in the E/P block copolymer than in the E/P random copolymer. The dependence of the relative content of the beta-form, as expressed by the K value, on crystallization temperature for the block copolymer is similar to that for polypropylene, i.e. the K value starts to decrease significantly only above 135-degrees-C. However, for the random copolymer it starts to decrease at a much lower crystallization temperature.