The purpose of this study was to observe the thermal expansion of the inlay waxes at temperature. Inlay pattern wax shows not only a high coefficient of expansion but also a tendency to warp or distort when allowed to stand unrestrained. The thermal expansion of inlay waxes was tested according to the treatment conditions for 10 minutes at $40^{circ}C$ The thermal expansion of inlay waxes at various temperatures was measured with an electro dial gauge. The results were as fellows: 1. It is shown that the rate of thermal expansion of wax A is 0.2%, wax B is 0.29%, wax C is 0.38%, and wax D is 0.22% at $40^{circ}C$ 2. It is shown that the coefficient of thermal expansion of wax A is $106{ imes}10^{-6}/^{circ}C$, wax B is $152{ imes}10^{-6}/^{circ}C$, wax C is $199{ imes}10^{-6}/^{circ}C$, and wax D is $116{ imes}10^{-6}/^{circ}C$ at $40^{circ}C$ 3. The thermal expansion of the inlay waxes at $40^{circ}C$ was shown to increase in the order of wax C, B, D, A.