Aryl and alkyl substituted 3- and 5-nitroisoxazole derivatives were prepared from the appropriate 3- and 5-nitro-4,5-dihydroisoxazoles using manganese(IV) oxide as oxidizing agent. Some of the 3-nitro-4-substituted isoxazoles were prepared directly by reaction of 2-substituted 3-bromo-l-halopropanes with sodium nitrite.