The main topic of this final work is temperature field during steady heat conduction in a sphere with heat source. At the beginnig of this final the basic terms , such as temperature, heat, heat exchane, temperature field and temperature gradient are explaned. Also in this introduction part, the Fouriers law is defined, as well as the coefficients such as thermal conductivity, thermal diffusivity and convection heat transfer coefficients. The second part of work is based on the derivation of the differential equation of heat conduction and boundary conditions. In the main part of the final work, the expression for the temperature field in sphere is derived by solving the differential equation. After the expression is obtained, the temperature field in the sphere is calculated. An analysis of the temperature change as a function of the radius of the sphere is performed and the effect of thermal conductivity on the temperature at the center of the sphere is examined. According to the derived expression and given boundary conditions, the computer program for calculating the temperature change in a sphere is written using the EES (Engineering Equation Solver) computer program the calculation is preformed. Since the sphere has a heat source, it was expected that the highest temperature would be in the center of the sphere, which was confirmed by calculation. The temperature distribution from the center of the sphere to the outside is concave, which is shown in EES. By increasing the value of the coefficient of thermal conductivity, the temperature in the center of the sphere decreases and opposite, which is confirmed and shown by EES.