In order to finding of potent natural medication/agent which can kill giardial cysts in the interval between lysing of outer membrane of cysts due to exposure by acidic condition of stomach and their encystation in proximal small intestine, In-vitro antigiardial activity and GC-MS analysis of Eucalyptus globulus and Zingiber officinalis against Giardia lamblia were studied in simulated condition to human’s body singly and in combination. Essential oils were extracted and their chemical components were identified via GC-MS method. After purification, cysts were exposure to acidic condition and were challenged by different concentrations of essential oils in simulated condition to human’s body. Percentages of inactivated (killed) cysts as efficacy of antigiardial activity were calculated and analyzed statistically. Presence of 1,8-eucalyptol, α-pinene, α-terpineol acetate, etc. in essential oil of E. globulus and presence of geraniol, α-zingiberene, (E,E)-α-farnesene, etc. in Z. officinalis essential oil were identified. Highest antigiardial activity (73.55%) was observed for eucalyptus essential oil in time 480 minutes after exposure. Efficacies of ginger and combined essential oils were different in different times. This study shows considerable antigiardial activity for both of essential oils singly and in combination together against giardial cysts. In-vivo study of protective effect of these essential oils against giardiasis can be considered as a subject for next studies.