Abstract: The yields of hydrazoic acid caused by the radiolysis of mono methylhydrazine (MMH) and β hydroxyethyl hydrazine (HEH) are determined by Fourier transform infrared spectroscopy and spectrophtometry. As a comparison, the yield from the hydrazine is also determined. The yield values at 10～500 kGy of the absorbed dose are 0.1～0.4 and 0.1～3.3 mmol·L -1 for the 0.2 mol·L -1 MMH and 0.2 mol·L -1 HEH solutions without and with 3 mol·L -1 HNO 3, respectively, and 0.2～57 mmol·L -1 for 0.2 mol·L -1 hydrazine solution with 3 mol·L -1 HNO 3. At the given experimental conditions, the yields from the MMH and HEH solutions are much lower than those of hydrazine solution and the explosion limit of hydrazoic acid. It is concluded that the small amount of produced hydrazoic acid for the MMH and HEH is probably related to the existence of the hydrazine as the impurity in MMH and HEH solution.