A liquid droplet in contact with a solid surface was simulated by the molecular dynamics method, in order to study the microscopic aspects of the liquid - solid contact phenomena and phase-change heat transfer. Measured ''contact angle'' was well correlated by the depth of the integrated potential of the surface. The layered liquid structure near the surface was also explained with the integrated potential field. Furthermore, evaporation and condensation through the droplet were simulated by preparing two solid surfaces with temperature differences on the top and bottom of the calculation domain. Overall heat flux and temperature distributions of droplets were measured.