The principal objective for our study was to evaluate the efficacy of Saccharomyces boulardii against Giardia  lamblia infection and investigated  the mechanism of this anti diarrheal effect on electrolyte (sodium,potassium and chloride) changes compared with metronidazole by using mice models.A single oral dose of S.boulardii of up to 5 x106cfu/0.1 of viable cells reduced parasite appear in feces and disappear completely at the 7th day compared with metronidazole the cysts parasite continued till 8th day. The yeast also caused increased potassium and sodium while decrease chloride level in serum. The histo morphological study findings showed in the group which was given S. boulardii the majority of intestinal villi return to normal shape. These finding indicated  that S.boulardii may be effective  in treating giardiasis also  has specific  effects on electrolyte  secretary  response.