Development of nanocrystals during crystallization of an amorphous alloy Zr47Ni30Ti23 is studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Up on heating the amorphous ribbon in DSC, three exothermic peaks including a broad peak are observed. Stable nanocrystals embedded in the amorphous matrix form through primary crystallization. The nanocrystals have uniform sizes after prolonged annealing at 400 degreesC for 180 minutes. Ni plays an important role for the stability of the nanocrystals. Due to the Ni partitioning between the nanocrystals and the residual matrix, the crystallization temperature (T-xI) of the residual amorphous matrix increases as crystallization proceeds. The formation of nanocrystal-amorphous composites that have high microstructural stability is possible through the controlled crystallization of the amorphous alloy Zr47Ni30Ti23.