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Pulp and paper mill wastewater (PPMWW) contains high concentrations of recalcitrant compounds that cause toxicity to organisms. Advanced oxidation processes (AOPs) have the ability to degrade these compounds and reduce overall toxicity. Physicochemical characterization and Lactuca sativa toxicity test were conducted to compare the effectiveness of two post-treatments: UV/H 2 O 2 and photo-Fenton. A comparison of four phytotoxicity indexes was carried out. PPMWW from a Brazilian treatment plant was characterized by high values of phenols, color, integrated spectral area (ISA), and chemical oxygen demand (COD), and caused significant inhibition to seedling development. The use of both post-treatments allowed the removal of over 75% of phenols, color, ISA, and COD. Although UV/H 2 O 2 was more effective in removing phenols and ISA, photo-Fenton better reduced phytotoxicity. The most sensitive phytotoxicity indexes were RGIC 0.8 and GIC 80% , whereas SGC 0 , REC -0.25 and REC -0.50 better showed the effectiveness of the post-treatments. We suggest the combined use of two phytotoxicity indexes: one that evaluates the effects on seed germination and, another, on root elongation, e.g., SGC 0 and RGIC 0.8. Additionally, we recommend the use of ISA for monitoring programs of wastewater treatments because it is a cost-effective approach that allows narrowing down the search and identification of compounds present in complex mixtures. Image 1 • PPMWW was post-treated by two AOPs: UV/H 2 O 2 and photo-Fenton. • Phenols, ISA and COD correlated negatively with germination and root elongation. • UV/H 2 O 2 better removed phenols and ISA, but photo-Fenton better reduced toxicity. • The most sensitive phytotoxicity indexes were RGIC 0.8 and GIC 80%. • SGC 0 , REC -0.25 and REC -0.50 better showed the effectiveness of the AOPs. [ABSTRACT FROM AUTHOR]