A　nanocrystal　catalyst　Ag/ZnO　was　successfully　synthesized　using　a　simple　solvothermal　method　in　this　study.　This　catalyst　was　characterized　by　X-ray　diffraction　(XRD)　and　transmission　electron　microscopy　(TEM).　The　results　showed　that　this　catalyst　was　composed　of　metallic　Ag　and　ZnO.　The　photodegradation　of　methyl　orange　(MO)　was　investigated　in　aqueous　suspension　containing　Ag/ZnO　catalyst　under　UV　irradiation.　Liquid　chromatography　coupled　with　electrospray　ionization　ion-trap　mass　spectrometry　was　applied　to　the　analysis　of　the　samples　coming　from　the　photocatalytic　degradation　of　MO.　The　experimental　results　showed　that　there　were　four　intermediates　existing　in　the　photocatalytic　reaction.　MO　could　be　mineralized　in　the　Ag/ZnO　suspension　after　60　min　illumination.