The gastric mucosa is continuously exposed to various agents like food condiments, spices, alcohol, acids and drugs, some of which are implicated in the pathogenesis of gastric ulcer. Magnesium compounds commonly used as laxatives and antacids have been reported to prevent ulcer formation but the mechanisms underlying this potential is unknown. This study therefore seeks to evaluate the gastro-protective mechanism of magnesium in the stomach through its effect on the parietal and mucus cells. Thirty-six male albino rats divided into 6 groups of 6 rats each were used. Group 1 was control, Group 2 was ulcer induced and untreated, Group 3 was treated with 500mg/kg b.w magnesium alone, Group 4 was pre-treated with 500mg/kg b.w magnesium before inducing ulcer, Group 5 was pre-treated with 500mg/kg b.w magnesium and 20mg/kg omeprazole 4 hours before inducing ulcer, Group 6 was treated with 20mg/kg omeprazole 4 hours before inducing ulcer. Animals were sacrificed 6 hours after ulcer induction and their stomachs were removed for ulcer scoring and histological analysis. A significant reduction was observed in the ulcer scoring of magnesium pre-treated ulcerated rats (9.4±0.8) compared with ulcerated untreated (20.8±0.9) groups. Parietal cell count of magnesium pre treated ulcerated group significantly decreased (169.7±18.9) compared with ulcerated untreated group (310.5±34.7). Mucous cell count of magnesium pre-treated ulcerated group (264.6±8.3) significantly increased compared with ulcerated untreated group (170.0±17.7). This study shows that magnesium possesses anti-ulcerogenic properties due to its ability to reduce the number of parietal cell and increase mucous cell counts.