In order to investigate how far the temperature-dependent fluid properties and characteristic length influence the drag coefficient and the heat flux, a three-dimensional simulation study for a slip flow around an unconfined microspherical particle has been performed. Gas properties such as density, viscosity, conductivity, and mean free path were assumed to vary with temperature. Slip velocity and temperature jump at the gas particle interface were both treated numerically by imposition of the slip boundary conditions. The effects of variable gas properties and Knudsen number on momentum and heat transfer were also taken into account. It was concluded that for microflows with high heat transfer rates, the constant fluid properties approximation is very crude. In addition, the slip velocity and temperature jump affect the heat transfer in opposite ways: a large slip on the wall increases the convection along the surface, whereas a large temperature jump decreases the heat transfer by reducing the temperature gradient at the wall. Therefore, neglecting temperature jump will result in the overestimation of the heat transfer coefficient.