In order to improve properties of the casting zinc alloy, modification of the structure consisting in the change of the morphology of alloy structural constituents has been applied, primarily by reducing interfacial eutectic α'+ η, reduction in the size of structural constituents, as well as the effect of Ce on the change of the grain morphology of the solid solution with the aluminum matrix from the dendritic one to the tweed one. Thermal analysis of the crystallisation process allows accurate calculation of latent crystallization heat of various phases crystallising during solidification. Calculation of the abovementioned properties is based on the characteristic points determined in a differential curve [1]. Therefore it is very important to know how the changes of the cast structure in relation to the change of the cooling rate and Ce mass concentrations. The purpose of this research work is to investigate the thermo-derivative interdependences occurred in the analysed zinc with cerium added alloys using Universal Metallurgical Simulator and Analyzer (UMSA) [2].