This thesis shows thermal simulations of a water-cooled brushless electric motor. The simulations are defined on the basis of engine specifications and customer requirements. The purpose of the thesis is to explore the principle of the software, that we use for performing heat conduction numerical simulation. The goal of the work is to create reliable and realistic simulations, which will then be available to the customer and to the company, that makes motors. The theoretical part of the paper presents the general structure and types of electric motors. The basics and the laws of heat transfer are also presented. In the part of the research methodology, a numerical model with corresponding boundary and initial conditions is presented. The loads of the model are shown and the materials from which the components are made are also presented. The results of the analysis show the distribution of the temperature field within the electric motor and the efficiency of the cooling system.