A facile, efficient, precise and reliable method based on liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established to separate and determine two typical quinolone antibiotics (ofloxacin and lomefloxacin) and two typical sulfonamide antibiotics (sulfadimeisoxazole and sulfadimidine). The photocatalytic degradation effects, identification of intermediate products and decomposition pathways of these four antibiotics degraded by Bi2MoO6/Bi2WO6/MWCNTs composite catalyst were analyzed using the developed HPLC-MS/MS method. It was found that all four antibiotics can be synchronously decomposed with the ultrahigh removal rates of above 95 %. Three main degradation reactions of quinolones were detected: the decarboxylation of quinolones, the ring opening reaction of piperazine and the defluorination of C-F. The main decomposition reactions of sulfonamides included the sulfonamide bond( S-N) breaking at the active sites, the oxidation of the amino acids on the benzene rings, and the substitution and oxidation ring opening reaction of pyrimidine. This study not only developed a detailed isolation and identification method for the degradation pathways and mechanisms of mixed pharmaceutical pollutants, but also provides a superb photocatalyst for the removal of multiplex pharma-ceuticalpollutants. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.