Phase-imaging tapping-mode atomic-force microscopy (TM AFM) has been used to study the grain size of TiSi2 films. Presently, there are few reports in the literature on the application of the phase imaging technique for grain size characterization. In this study, very clear images of TiSi2 grains have been obtained and compared to transmission electron microscopy micrographs. For the first time, both triple point C54-TiSi2 nuclei and C49-phase grains have been clearly identified with this technique. C49 and C54-TiSi2 nuclei are about 50 and 15 nm, respectively at 650degreesC. The C49-to-C54 phase transformation of TiSi2 is confirmed by x-ray diffraction. This study demonstrated that TM AFM can be used for grain size characterization with high accuracy and efficiency.