The synergistic effect of gamma radiation with hydrogen peroxide (H2O2) for p-nitrophenol (PNP) decomposition in aqueous solution was evaluated. The PNP solution with initial concentration of 50 mg/L was irradiated in the presence of extra H2O2 at initial concentration of 0, 20, 40, and 80 mg/L. The experimental results showed that the decomposition of PNP conformed to the pseudo-first-order reaction kinetics under the applied conditions. When initial H2O2 concentration was in the range of 0-80 mg/L, higher concentration of H2O2 was more effective for the decomposition, mineralization and nitrogen release of PNP. However, the removal of total organic carbon (TOC) and total nitrogen (TN) was not as effective as that of PNP. Ammonia and nitrate were detected as the main inorganic nitrogen products of PNP decomposition without extra H2O2, whereas nitrate was considered as a final inorganic nitrogen product with extra H2O2 in the initial concentration range of 0-80 mg/L. Major decomposition products, including organic acids were identified by LC/MS and IC. Possible pathways for PNP decomposition by gamma radiation in aqueous solution were proposed. (C) 2010 Elsevier B.V. All rights reserved.