This study was carried out in Kaliobia governorate from April to December 1997 to investigate the occurrence of Giardia cysts in dogs, cats, rodents and possible implication in infantile diarrhea. A total of 400 faecal samples were collected from Stray dogs and cats, 300 from rats and mice as well as 400 from children affected with diarrhea at age group 1-10 years. The prevalence of Giardia cysts in faecal samples amounted to, 24% dogs, 11% cats, 19.66% rats and mice; 21.48% (Rattus rattus), 25.55% (Rattus norvegicus) and 9.33% (Mus musculus). Giardia lamblia cysts were found in 21% in children affected with diarrhea. Experimental infection of different species of rats and mice (Rattus rattus, Rattus norvegicus and Mus musculus) with Giardia cysts obtained from diseased children revealed no difference in morphological character of infective stage and emphasized the interspecies transmission concept of Giardia and its public health importance.