Giardia lamblia, a waterborne parasitic protozoa causing diarrhea and gastroenteritis, is transmitted to humans from untreated and treated water in the form of cysts. The ingestion of G. lamblia cysts is followed by the excystation of the cysts to trophozoites and subsequent colonization of the upper small intestine. In this study, the in vitro conditions for upper small intestine. In this study, the in vitro conditions for G. lamblia encystation were investigated to enhance the efficiency of cyst conversion and the resulting cyst density. The trophozoite of G. lamblia was cultivated to the late exponential growth phase, resulting in a high density of over $6{ imes}10^7{;}cells/ml$. The effects of pH, bile content, and induction time were evaluated; A cyst conversion of over 25% and 107 time were evaluated; A cyst conversion of over 25% and 107 cysts/ml were routinely obtained using the optimized encystation conditions including a slightly slkaline pH, 10 to 15 mg/ml of bile concentration, and 48-50 h of induction time.