Aims: the infection with Toxoplasma gondii parasite causes some dangerous diseases such as the disease toxoplasmosis in the human in the world. Therefore, the present work done to investigate some ultrastructure changes in the nuclei of cells of the liver in Toxoplasma gondii-infected male mice for both 3 months and 5 months. Results: The density of all chromatin types (prefrail, granular and associated nucleolus chromatin and extended chromatin) of nucleus in Toxoplasma gondii infected-mice for both 3 months and 5 months increased versus there control mice and it markedly increased in infected-mice for 5 months versus infected mice 3 months. the number of nucleoli in hepatocytes nucleus markedly increased in control 5 months versus control 3 months and not changed in Toxoplasma gondii infected-mice with time. Conclusion: Toxoplasma gondii Me49 strain-infection has stimulatory effect on the density chromatin distribution in normal hepatocytes nucleus and no effect on the number of nucleoli in hepatocytes nucleus but the age of animal increased the number of nucleoli in normal hepatocytes nucleus.