A hydroponic experiment was carried out to study the effects of different concentrations of sulfur (0.01-32 mmol/L) on chlorophyll contents and chlorophyll fluorescence parameters of flue-cured tobacco leaves at maturation stage. Chlorophyll a and chlorophyll b contents of flue-cured tobacco leaves at maturation stage gradually increased with increasing concentrations of sulfur, but differences among the treatments were not significant. Chlorophyll a/b values of flue-cured tobacco leaves at maturation stage had no regular change but chlorophyll a/b values in the 0.01-8 mmol/L concentrations of sulfur were slightly higher than those in the 16 and 32 mmol/L concentrations of sulfur. As the sulfur concentration increasing from 2 to 32 mmol/L, there were decreases in the effective quantum yield (EQY), the maximum quantum yield of PSⅡ photochemistry in the dark-adapted state (F_v/F_m), and the photosynthetic electron transport rate (ETR) of flue-cured tobacco leaves at maturation stage, but increases in nonphotochemical quenching (NPQ), basal quantum yield of nonphotochemical quenching (F_o/F_m), PSⅡ water-splitting apparatus inactivation (F_o/F_v), and the degree of reaction center closure (1-qP). The plastoquinone pool (F_v/2) of flue-cured tobacco leaves at maturation stage in the 2 mmol/L concentration of sulfur was lower than that in the 4 mmol/L concentration of sulfur but higher than those in the 8-32 mmol/L concentrations of sulfur. The curves of F_v/2 of flue-cured tobacco in 8-32 mmol/L concentrations of sulfur were almostly overlapped. The EQY, and ETR of flue-cured tobacco leaves at maturation stage in the 0.01 mmol/L concentration of sulfur were lower than those in the 2-8 mmol/L concentrations of sulfur, but higher than those in the 16-32 mmol/L concentrations of sulfur. The F_v/F_m of flue-cured tobacco leaves at maturation stage in the 0.01 mmol/L concentration of sulfur was lower than those in the 2-4 mmol/L concentrations of sulfur but higer than that in the 32 mmol/L concentration of sulfur. There were not significantly different in the F_v/F_m among the 0.01, 8 and 16 mmol/L concentration of sulfur. The curves of 1-qP, F_o/F_m and F_o/F_v of flue-cured tobacco leaves at maturation stage in the 0.01 mmol/L concentration of sulfur were intertvined with 8 and 16 mmol/L concentrations of sulfur and higher than those in the 2-4 mmol/L concentrations of sulfur but lower than those in the 32 mmol/L concentration of sulfur. The NPQ of flue-cured tobacco leaves at maturation stage in the 0.01 mmol/L concentration of sulfur were significantly higher than those in the 2-4 mmol/L concentrations of sulfur. Similarly, the NPQ in the 0.01 mmol/L concentration of sulfur was higer than those in the 8-32 mmol/L concentrations of sulfur at photosynthetic active radiation (PAR) range 0-500 μmol · m^-2 · s^-1 but lower than those in 8 and 16mmol/L concentrations of sulfur at photosynthetic active radiation over 500μmol · m^-2 · s^-1. The F_v/2 of flue-cured tobacco leaves at maturation stage in the 0.01 mmol/L concentrations of sulfur was lower than that in the 4 mmol/L concentration of sulfur, but higher than those in the 2 mmol/L and the 8-32 mmol/L concentrations of sulfur. These results suggested that the decreases in the EQY, F_v/F_m, and ETR of flue-cured leaves at maturation stage in the 0.01 mmol/L concentrations of sulfur did not result from a decreased plastoquinone pool, but from an increase in the degree of reaction center closure. In the 16-32 mmol/L concentrations of sulfur, the decreases in EQY,F_v/F_m, and ETR resulted from a combination of increased degree of reaction center closure and a decreased plastoquinone pool.