The transformation behavior of the ion-beam-induced amorphous Pt 2Si3 alloys has been studied by using resistivity measurements. Two distinct stages of transformation were observed as revealed by a rapid change of resistivity with increasing annealing temperature. In the first state a transfrom from the amorphous to a metastable crystalline Pt 2Si3 phase occurred in a narrow temperature range around 400°C. The second stage, which appeared gradually near 550°C, involved the transformation to the equilibrium two-phase state of PtSi and Si. The kinetics of the amorphous to metastable crystalline transformation has been determined by isothermal treatment over the temperature interval 376-392°C. The results are interpreted in terms of a classical nucleation and growth mechanism with a t4 (time) dependence and an apparent activation enthalpy of (108±5) kcal/mol. The microstructure of the alloys at various stages of transformation was studied by transmission electron microscopy and diffraction. The correlation between the kinetics and the microstructures of the alloyed layers is given and discussed.