The topic of this paper is determination of effective case depth. In the continuation of the paper, the general division of heat treatment is presented, as well as the description of individual thermochemical treatment procedures: nitriding, carbonitriding, nitrocarburizing and sulfonitrocarburizing. Since the topic is cementation, the cementing process and cementing phases, which are carbonization, hardening and relaxation. The specific details are elaborated in the following paragraph. After getting acquainted with thermochemical treatment and individual processes, the processes of carburization in solid, liquid and gaseous medium are elaborated in more detail. Then, the properties of cemented layers and methods for determining of effective case depth are described, as well as application of cementation procedures. Cementing of C15 steel was performed in experimental part. Carburization was carried out in a solid medium at 920 °C for 4h. Carburization was followed by hardening which is consisting of austenitization and quenching. The austenitization temperature was 900 °C for 0,5h, after which the sample was quenched in water. After hardening, the sample was relaxed at low temperature at 180 °C for 1,5h and then cooled in air. After cementation, the microstructure was analyzed, and the cross – sectional hardnesses were measured. Based on the hardness, the effective layer thickness was determined.