Abstract: 3-Garbamoyl-5-methyl-isoxazole (Ⅰ) reacts with aqueous sodium hypochlorite solu-tion to give 5-methyl-3-aminoisoxazole (Ⅱ) through the Hofmann rearrangment. In this reaction a new by-product is observed and is shown to be 5,5'-dimethyl-3, 3'-azo-isoxazole (Ⅲ) by chemical methods and spectral analyses.It is possible that the by-product (Ⅲ) produced is due to the presence of excess of sodium hypochlorite which oxidizes amino-product (Ⅱ) to azocompound (Ⅲ).