N,　N-dimethylhydroxylamine　(DMHA)　is　a　new　salt-free　reductant　used　in　spent　fuel　reprocessing,　this　paper　reports　the　effect　of　HNO2　on　-ray　radiolysis　and　radiolytic　products　of　DMHA　in　nitric　acid　medium.　DMHA　concentration　in　irradiated　samples　decreases　with　the　increasing　dose　and　initial　HNO2　concentration,　and　the　radiolytic　rate　of　DMHA　is　lower　than　21%　at　10kGy　supposed　to　be　the　maximum　dose　absorbed　by　the　reagent　during　the　U/Pu　separation　and　the　Pu　purification.　The　main　radiolytic　products　are　H-2,　CH3NHOH,　HCHO,　and　HCOOH,　and　their　quantity　increases　with　the　dose　and　initial　HNO2　concentration.