<p>Generally, Fe(II) has an efficiently catalytic activity toward peroxymonosulfate (PMS), but the slow conversion of Fe(III) to Fe(II) and production of iron sludge impede the practical application of Fe(II)/PMS system. In this work, ascorbic acid (AA), a complexing agent and reductant, was introduced to Fe(III)/PMS process to facilitate the Fe(III) reduction. The decoloration of rhodamine B (RhB) was obviously enhanced in Fe(III)/PMS process with the addition of AA. Fe(III)-AA complex was firstly generated in Fe(III)/AA/PMS process via the complexation and then was reduced to Fe(II), which could catalyze PMS to yield oxidative species. Fe(IV), sulfate radical (SO₄^•−) and hydroxyl radical (^•OH) were the working oxidants for RhB decoloration in this system, and SO₄^•− played a major role. Increasing Fe(III), AA or PMS dosage was beneficial to RhB decoloration, but their excessive concentration would hinder RhB decoloration. The existence of HCO₃⁻, SO₄²⁻ or FA in this system showed an inhibition effect on RhB decoloration, while a facilitation effect was obtained when the high concentration of Cl⁻ was present. This research offers a way to improve PMS activation by Fe(III) and a technology for eliminating the refractory organic pollutants from the contaminated water.</p>