Abstract: The study with solution culture showed that under sulfur deficiency,the net photosynthetic rate (Pn),photorespiration rate (Pr),photosynthetic pigment content,soluble protein content,original fluorescence (Fo),photochemical efficiency (Fv/Fm),maximum fluorescence (Fm),and electron transmit rate (ETR) ofCitrus sinensis Osbeck leaves declined markedly,while Pr/Pn increased obviously.The depress of C.sinensis Osbeck leaves photosynthetic ability under sulfur deficiency could be resulted from the disfigurement of chloroplast growth or the deficiency of characterizing functional protein.