The relationships between lateral force and viscoelastic properties of amorphous polymer surfaces with Tg’s lower and higher than room temperature (295 K, RT) and their blend systems have been studied on the basis of lateral force microscopic (LFM) measurement. Under the conditions of scanning rate of 10(2) - 10(5) nm sec(-1), normal load of 5 nN and RT, the lateral forces of poly(methyl methacrylate) (PMMA) and polyisoprene (PI) homopolymers with Tg’s fairly higher and lower than RT, respectively, did not depend on the scanning rate. Whereas, the lateral force of poly(methyl acrylate) (PMA) with Tg less than or equal to RT decreased with an increase in the scanning rate. Also, poly(vinyl acetate) (PVAc) with Tg greater than or equal to RT showed slight dependence on the scanning rate. The scanning rate dependence of lateral force was similar to the frequency dependence of mechanical loss modulus. The results indicate that the magnitude of lateral force strongly depends on the state of thermal molecular motion. The lateral force-viscoelastic properties of miscible polymer blends was also investigated by LFM.