The interfacial photoinduced electron transfer and related secondary photochemical behaviour in the system of ZnS/CdS co-colloid superfine particles were studied by means of ESR and fluorescence spectroscopy techniques. The photoinduced charge-separation and the radical intermediates produced in the secondary redox reactions initiated via charge separation, as well as the mechanism of reaction processes, were investigated in detail through simultaneous excitation of two colloid components or only one of them. Research results indicated that, as E_(g(ZnS))>E_λ>E_(g(CdS)), only CdS in co-colloid system might be excited. The transfer process of electron from the conduction band of CdS to the conduction band of ZnS is forbidden, and under the excitation wavelength range used, the electron transfer of cocolloid system was impossible, thus the photo redox reactions of the substrate in co-colloid system had no obvious difference from those reactions happening in single colloid system. While the excitation wav The interfacial photoinduced electron transfer and related secondary photochemical behavior in the system of ZnS / CdS co-colloid superfine particles were studied by means of ESR and fluorescence spectroscopy techniques. The photoinduced charge-separation and the radical intermediates produced in the secondary redox reactions initiated via charge separation, as well as the mechanism of reaction processes, were studied in detail through simultaneous excitation of two colloid components or only one of them. Research results indicated that, as E_ (g (ZnS))> E_λ> E_ (g The transfer process of electron from the conduction band of CdS to the conduction band of ZnS is forbidden, and under the excitation wavelength range used, the electron transfer of cocolloid system was impossible thus the photo redox reactions of the substrate in co-colloid system had no obvious difference from those reactions happening in single colloid system. While the excitation wav