Abstract: Certain characteristics concerning the growth and multiplication of Giardia lamblia were observed in the course of monoxenic and axenic cultivation of the parasite. The organism used for monoxenic culture originated from a local giardiasis patient. Cysts from patient fecal specimen were isolated by sucrose gradient centrifugation and then used to infect rabbits. Trophozoites recovered from intestinal mucosa of the infected animal were cultivated at 37℃ together with a small amount of Saccharomyces cerevisiae. They grew luxuriantly and formed a monolayer upon the wall of the culture tube at about 24 hours. Thereafter, yeast cells gradually overgrew the parasite whose number becomes less and less, until very few remains at the fifth day.Strain of G. lamblia and TPS-1 medium used in the axenic culture was supplied by Dr. Visvesvara (CDC, Atlanta). Certain characteristics of the multiplication of the parasite, particularly those concerning the binary fission process, were observed under scanning electron microscope and optic microscope during the course of cultivation which lasted 5 months. The morphological changes at various stages of binary fission of the organism were described.