In this study, the aim was to determine the production of Cu/Zn SOD (SOD1) enzyme in the heart, liver, and pancreas of rats administered Homalothecium sericeum extract. The effect of the use of moss extract has not been studied for Cu/Zn SOD enzyme production in different tissues of rats or for the cytotoxic effects on these tissues. In our study, 50 mg/kg (Group I, n: 6), 100 mg/kg (Group II, n: 6), 300 mg/kg (Group III, n: 6) and 500 mg/kg (Group IV, n: 6) doses of moss extract and 1 ml of distilled water (Group V, n: 6) were administered by gavage to 30 female rats for 30 days. Cu/Zn SOD enzyme immunoreactivity was investigated in liver, heart and pancreas tissues depending on the increase in moss extract dose. To determine Cu/Zn SOD immunoreactivity, after the application of Cu/Zn SOD primary antibodies using immunohistochemical staining methods, DAP was used as coloring and hematoxylin was used as inverse dye. The stained tissue samples were evaluated with an image analysis system under the research microscope and the study used the Kruskal-Wallis Test, one of the nonparametric tests, to detect the differences between the groups statistically.