Effects of Co2+ on fluoresence emission spectra at room temperature,activity of DCIP photoreduction and polypeptide compositions of thylakoid membrane were studied.The results showed that fluoresence emission spectra at room temperature was changed after Co2+treatment: intrinsic fluoresence spectra at room temperature upon excitation at 278 nm and 295 nm was decreased at the Co2+concentration below 15 mmol/L and increased at the Co2+concentration above 15 mmol/L;Chlorophyll fluoresence spectra at room temperature upon excitation at 436 nm and 475 nm was decreased;The inhibition of DCIP photoreduction activity and the changes of polypeptide compositons of the thylakoid membrane were observed as a result of Co2+ treatment.