The sequence of phase formation during mechanical alloying of chromium and silicon powders has been studied using high-energy ball milling of mixtures of elemental powders with different Si/Cr atomic ratios. X-ray diffactometry and transmission electron microscopy have been utilized to identify the phases and to characterize the microstructure of the powders. All four equilibrium phases in the Cr-Si system can form. With a Si/Cr atomic ratio equal to or higher than 3/5, CrSi2 is always the first phase to form, and then CrSi2 can react with chromium to form CrSi or Cr5Si3, depending on the Si/Cr atomic ratio. This is similar to the sequence of phase formation during annealing of multilayer chromium and silicon thin films. However, with low Si/Cr atomic ratio close to 1/3, Cr3Si is the first and only phase to form during mechanical alloying.