This work proposes a mathematical modeling and numerical simulation of a gypsum rotary kiln with indirect oil heating in a three-dimensional transient regime. The mathematical model was based on Fourier's Law as a constitutive relationship and the principle of energy conservation, applied to a control volume in cylindrical coordinates. Furthermore, a bed homogenization model was used to represent the most realistic condition of the physical phenomenon since some rotary kilns have internal fins that aim at homogenizing the gypsum temperature during calcination. This work intends to fill the gap found in heat transfer processes on rotary kilns in transient regime considering three dimensions positions, to have an accurate projection of the temperature profile of the kiln and also, given by the numerical model, the possibility of a tool that can be used to the optimization of the control system of rotary kilns considering the actual demand of the material in production, leading to the best energy performance of the equipment's activation source, as well as reaching the temperatures and processing time of the product. The numerical simulation results revealed reasonable agreement with the experimentally determined calcination process in rotary kilns. Furthermore, a parametric analysis of the influence of the mixture on the temperature fields and the calcination time was carried out to verify the energetic balance of the rotary kiln.