In a laboratory study, decolourisation of four reactive dyes (Cibacron Yellow C5G, Remazol Blue RGP, Remazol Red RGP and Remazol Golden Yellow RGP) by modified photo-Fenton (UV-vis/ferrioxalate/H2O2) process under irradiation with sunlight was examined. Over 90 decolourisation occurred in 90-120 min for dye concentrations of 20, 50 and 100 mg/L, indicating the effectiveness of ferrioxalate complexes in decolourisation of even strongly coloured solutions. The study has demonstrated that modified photo-Fenton process is an effective process for decolourisation of reactive dyes. The process is useful for treatment of dyehouse waste in tropical and equatorial regions where sunlight is abundant.