High-resolution mass spectrometry combined with liquid chromatography (LC-HRMS) was employed tocomprehensively investigate transformation pathways and transformation products (TPs) formation during thedegradation of ceftazidime (CAZ). The degradation of CAZ was investigated using advanced oxidation processes(AOPs), including heterogeneous TiO₂ photocatalysis, MOF-based photocatalysis, and homogeneous treatmentswith hydrogen peroxide (HP) or persulfate (PS). TiO₂-mediated photocatalysis achieved complete CAZ removalwithin 60 min, with reaction rates enhanced by increased catalyst loading or oxidant addition, whereas excessiveHP concentration slowed degradation. MOF-based photocatalysis showed limited activity, although oxidantsimproved reaction kinetics. Homogeneous photocatalytic treatments also efficiently degraded CAZ, with higheriron or oxidant concentrations accelerating the process. LC-HRMS analysis enabled the confident elucidation ofeighteen TPs, seventeen of which are reported here for the first time for ceftazidime degradation, classified as N-alkylated pyridinium derivatives, aminothiazole-ring derivatives, and alkyl sulfates. Accurate-mass measure-ments and HRMS-based structural interpretation revealed key transformation pathways during CAZ oxidation.Total organic carbon (TOC) measurements indicated superior mineralization with TiO₂, followed by homoge-neous treatments. ECOSAR-based toxicity predictions suggested low ecotoxicity for most TPs, except the parentcompound and TP273, which exhibited potential toxicity toward Daphnia magna. Overall, photocatalytic AOPseffectively degrade CAZ and its TPs, with HRMS-supported TP elucidation demonstrating that TiO₂-based het-erogeneous photocatalysis providing the highest mineralization and lowest predicted ecotoxicity.