Electrochemically activated peroxymonosulfate with mixed metal oxide electrodes (EA-PMS-MMO/MMO) is an emerging advanced oxidation process. It performed well on the degradation of sulfadiazine (SDZ), whose removal rate reached 81.13% within 30 min. Both the MMO anode and cathode played an irreplaceable role in PMS activation. HO•, SO4•-, O2•- and 1O2 were confirmed to be the major reactive species in the system, among which 1O2 was the most abundant. The generation mechanism of the reactive species and the overall mechanism of the system were proposed. Four degradation pathways of SDZ were speculated based on density functional theory. The acute and chronic toxicity of SDZ and its degradation intermediates was evaluated by the quantitative structure-activity relationship method, and the overall toxicity was significantly reduced after the degradation by EA-PMS-MMO/MMO. The results show that EA-PMS-MMO/MMO affords a reliable technology for the degradation of organic contaminants and has promising potential for application. Display omitted •Both the MMO anode and cathode play an irreplaceable role in the activation of PMS.•1O2 was the most abundant reactive specie among HO.•, SO4•-, O2•- and 1O2.•The degradation pathways of SDZ are speculated based on DFT and LC-MS detection.•The toxicity of SDZ can be significantly reduced after full oxidation by EA-PMS-MMO/MMO.