A lateral force microscope (LFM) was used for studying the surface morphologies of SrBi2Ta2O9 thin films with varying post-annealing temperature. Specimens were prepared onto platinized silicon wafers by the sol-gel method and post-annealed at 600-800 degrees C. Non-ferroelectric matrix phases were found for specimens annealed below 700 degrees C, which were confirmed by the measurement of X-ray diffraction (XRD) patterns. The friction coefficients between the surface of ferroelectric grain and non-ferroelectric matrix, and the silicon nitride tip, were determined from the line profile of the LFM images. The measured coefficients of friction for a tip on grain and matrix are 0.19 +/- 0.08 and 0.28 +/- 0.08, respectively. In the LFM images, the matrix phases decreased with increasing post-anneal temperature and the surfaces of the specimens annealed above 700 degrees C were filled with SET grains which were consistent with the XRD results. Ferroelectricities of these specimens were confirmed by the measurement of polarization held hysteresis loops.