Aims The objective of this study was to assess the probiotic potential of genuine strains of Bifidobacterium longum 5(1A) and Weissella paramesenteroides WpK4, in experimental giardiasis. Methods and Results The bacteria were administered orally to gerbils (Meriones unguiculatus) 10 days before oral infection with trophozoites of Giardia lamblia. After 7 days of infection, the animals were euthanized and portions of the duodenum were processed for histopathologic, histochemical and morphometric assessment. The height of the intestinal crypts and crypt/villi ratio were higher in infected groups (P < 0 center dot 05) than in noninfected groups. The area of mucus production was higher (P < 0 center dot 05) in infected animals pretreated with B. longum 5(1A )than in other groups. The parasitic load of the animals that received both bacteria decreased significantly (P < 0 center dot 05) compared to the ones of the control group. Conclusions Our results suggest a probiotic function of B. longum 5(1A )and W. paramesenteroides WpK4 and may result in their use as a prophylactic and therapeutic alternative for promoting human and animal health. Significance and Impact of the Study Bifidobacterium longum 5(1A) and W. paramesenteroides WpK4 may constitute prophylactic alternatives, reversing the emergence of side effects and resistance observed in the conventional treatment of giardiasis.