The aim of the study was to evaluate the effect of zinc and manganese levels in the diet for laying hens on eggshell percent, thickness, density and eggshell breaking strength. Experiment was carried out on 90 Hy Line Brown hens, from 25 to 70 weeks of age, allocated to 10 experimental groups, each containing 9 hens individually caged on wire-mesh floor. All layers were fed the same basal diet, containing recommended amounts of all nutrients, except zinc and manganese, because vitamin-mineral diet without these microelements was used. In the experimental groups basal diet was supplemented with increasing levels of Zn and Mn (as ZnO and MnO forms), in the amounts from 0 to 100 mg/kg. The used levels of addition of the studied microelements had no effect on laying performance. Supplementation of basal diet with Zn and Mn did not influence eggshell percent, thickness and density. Addition of Mn to the basal diets increased the eggshell breaking strength in second phase of laying cycle. Enriching the basal diet with Zn had no effect on this parameter. In all experimental groups there was highly significant, negative correlation between hen age and eggshell breaking strength. Based on linear regression equations it was found that diet supplementation with 20 mg Mn/kg reduced negative effect of layer age on shell breaking strength by 43%, while the simultaneous addition of 20 mg Zn/kg and 50 mg Mn/kg - by 46%.