Abstract: Pulse radiolysis of aqueous methylhydrazine solutions under different conditions was studied. The main characteristic peaks in these transient absorption spectra were attributed and the build-up/decay trends of several transient species were investigated. The reaction product of •OH radical and methylhydrazine is CH₃•NNH₂ radical with a rate constant of (2.4±0.1)×10¹⁰mol^-1•L•s^-1. The reaction product of e_aq^- and methylhydrazine is CH₃•NHNH₂ radical with a rate constant of (2.7±0.2)×10⁸ mol^-1•L•s^-1.