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Abstract. The structure and thermomechanical properties of Ni-Ti-Cu alloy partially crystallized rapidly quenched ribbons were studied. The technique of controlled isothermal annealing of the initially amorphous ribbons in the differential scanning calorimeter was used for preparation of the samples with determined relations of extracted thermal energies to the full crystallization energy. The thermomechanical properties of the ribbons were studied in temperature interval -100..100 C. It was found that temperature dependence of bending deformation demonstrates hysteresis for the samples with more then 29% of crystalline phase. The shape memory effect manifests itself in these samples. The value of the reversible strain rises with the crystalline phase increase. The HRTEM studies show that rare crystallites have spherical shape in samples with 15% crystalline phase. Their sizes vary from 100 to 1000 nm. The DSC studies show peaks corresponding to the direct and reverse martensitic transformation at temperatures T am = 15 C and T ma = 29 C. The concretion of crystallites with plane boundaries formation was observed in samples with 29% of crystalline phase. The martensitic transformation is suppressed in crystallites less than 300 nm at room temperature. Unlike this in b technique. The model for the explanation of the observed phenomena is discussed.