Influences of several different kinds of flocculating agent on photosynthetic bacteria Rhodobacter sphaeroides were assessed by analyzing settling performances and strength of bioflocculates. From the results, polychlorinated alumina (PAC) was finally selected as a flocculating agent to accelerate formation of granular sludge of Rhodobacter sphaeroides. Tests gave the dose of PAC in the range of 140-160 mg/L. When the dose of PAC was 150 mg/L, granulation was the most effective. The degradation efficiency and reaction parameters were investigated on treating chlorobenzene in water by granular sludge of Rhodobacter sphaeroides. The results showed that the optimal conditions of treatment for chlorobenzene in water by granular sludge of Rhodobacter sphaeroides were aerobic condition, temperature 30oC and pH 7.0.