Cyclization of oxime with different aldehydes and ketones under basic condition led to the formation of new dioxazole derivatives and the structure was elucidated by spectral data. The effects of diaoxazoles on the inhibition of growth of Entamoeba histolytica and Giardia intestinalis in vitro have been determined, and selected compounds further investigated for their toxicity. SAR showed that the compounds with 5-nitrothiophene group at the 3-postion of the diaoxazole ring were more active than those with the p-toluene group at the same position. It is interesting to note that the compounds found active against E. histolytica were not found active against G. intestinalis. Toxicity studies showed that the compound 8 and 9 were non-toxic against Vero cell line ATCC CCL-81.