Generally, pile foundation is typically chosen to support heavy structures. However, the developments of expressions to determine the pile capacity is usually based on fully saturated and completely dry conditions. In fact, almost 40 percent of natural soils on the earth surface are in an unsaturated state. Thus, in this paper, an expression for pile capacity in homogeneous unsaturated sand layer is developed. The simulations using developed expression are performed and discussed. Typical results show that the pile capacity and the factor of safety are affected by matric suction. However, the influence of matric suction may be ignored for a long pile.