Phosphite is an important intermediate of the phosphorus cycle. Its life in environment is related to its oxidation rate. This paper investigated the photooxidation of phosphite in aqueous solution in the presence of ferric and oxalate ions under a Xe lamp. The photooxidation of phosphite followed pseudo-first-order reaction kinetics. The kinetics constant of 100 mu mol L-1 phosphite was 0.0039 min(-1) at pH 3 and Fe(III)/Ox 10.0/100.0 mu mol L-1. The photooxidation was dependent upon the pH value, phosphite/ferric/oxalate concentration, and light intensity. The decrease of phosphite coincided with the increase of phosphate. The addition of 2-proponal, NaN3 or furfuryl alcohol inhibited the photooxidation of phosphite, which indicated that the yielded reactive oxygen species played an important role in the oxidation of phosphite. The results contribute not only to predict the longevity of phosphite in the aqueous solutions, but also to understand the transfer of phosphite in P cycle. (C) 2015 Elsevier B.V. All rights reserved.