The microstucture of metastable C49-TiSi2 was studied by high-resolution transmission electron microscopy in a bilayer thin film of Ti and Si annealed at 700 °C. Large grains (300-400 nm) of C49-TiSi2 phase with high density of stacking faults on (010) planes were observed. A preferred orientation among the C49-TiSi2 grains was identified, and the grains were aligned along the  with slight misorientation. The diffraction pattern from the metastable TiSi2 showed continuous streaks superimposed by discrete spots along hk0 reciprocal lattice rows, indicating the presence of polytypism. Lattice imaging of polytypic TiSi 2 has been obtained and it showed that the structure is nonperiodic and one dimensionally disordered due to the stacking faults. The finding of metastable TiSi2 associated with polytypism suggests that its structure could be conveniently represented by various stackings of atomic planes along the  direction. An atomic model is proposed to explain the origin of polytypism. It is shown that the arrangement of atoms in C49-TiSi 2 structure has four equivalent positions.