The effectiveness of photo-Fenton-like process to degrade aqueous polyacrylic acid (PAA) is investigated in a batch recirculation system using two photoreactors in series. The response surface methodology (RSM) using the Box–Behnken experimental design combined with quadratic programming is employed for the experimental design, the statistical analysis and the optimisation. The effects of the initial concentration of PAA, the initial concentration of H2O2:Fe3+, pH and the recirculation rate on the percent removal of total organic carbon (TOC)and the ‘pseudo’-second order rate constant as the process responses are studied. The statistical analysis of the results indicates a satisfactory prediction of the system behaviour by the developed quadratic models. Optimum operating conditions to maximise the percent TOC removal are also determined.