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Electrochemical degradation of sulfamethoxazole (SMX) and its metabolite acetyl-sulfamethoxazole (Ac-SMX) by Ti/SnO2-Sb/Er-PbO2 were investigated. Results indicated that the electrochemical degradation of SMX and Ac-SMX followed pseudo-first-order kinetics. The rate constants of SMX and Ac-SMXwere 0.268 and 0.072 min-1 at optimal current density of 10 and 14 mA/cm2, respectively. Transformation products of SMX and Ac-SMX were identified and the possible degradation pathways, including the cleavage of S-N bond, opening ring of isoxazole and nitration of amino group, were proposed. Total organic carbon removal of SMX was nearly 63.2％ after 3 h electrochemical degradation. 22.4％ nitrogen of SMX was transformed to NO3-, and 98.8％ sulfur of SMX was released as SO42-. According to quantitative structureactivity relationship model, toxicities of SMX and Ac-SMX to aquatic organisms significantly decreased after electrochemical degradation. Electric energy consumption for 90％ SMX and Ac-SMX degradation was determined to be 0.58-8.97 and 6.88-44.19 Wh/L at different experimental conditions, respectively.Compared with parent compound SMX, the metabolite Ac-SMX is more refractory and toxic, which emphasizes the importance of taking its metabolites into account when investigating the disposal of pharmaceuticals from wastewater.