AbstractFour mixtures of 1,4‐trans‐polyisoprene with methyl oleate (vol. fraction of polymer: 0,696 to 0,092) were prepared, and a dilatometric study of the crystallization kinetics was carried out in a convenient temperature range. The polymer was found to crystallize in the form of its high melting polymorph. The amount of secondary crystallization was less compared to that observed earlier for undiluted polymer. Formation of crystalline phase was found to be more difficult. In the absence of nucleation and growth data, the actual differences in interfacial energies required for nucleation and growth could not be estimated quantitatively, however, the experimental results indicate that compared to the bulk system, the energy requirements for the primary nucleation act in case of mixtures are higher. The interfacial energy σ′e (calculated after neglecting the transport term) was in the range 2309–2356 cal/mol for all the mixtures and showed appreciable variation with change in polymer concentration. A molecular interpretation of the possible mechanism operating in the crystallization of mixtures is given.