An autotrophic denitrification process using reduced sulfide as electron donor in anaerobic system is proposed as an efficient and cost effective alternative to conventional heterotrophic denitrification for low C/N ratio wastewaters and for simultaneous removal of sulfide and nitrate. A suspended culture of Thiobacillus denitrificans bacteria was fast and efficiently established in anaerobic system. 5 series bioaugmented anaerobic systems with different N/S ratio synthetic influent were set up. Sulfide, nitrate, sulfate, and nitrite concentration in the effluent at every 3 hours were measured after 15 day. The primary objective was to investigate the characteristic of autotrophic denitrification and sulfide oxidation, and to reveal the mechanism of autotrophic denitrification process using reduced sulfide as electron donor in bioaugmented anaerobic system. 90% removal efficiency of sulfide was observed after 3 hours and removal efficiency of sulfide had no reference to N/S ratio. The rate of sulfide oxidation was 20-24 g x (m3 x h)(-1), which was 10 times higher than that have been reported in the literatures. Maximum removal efficiency of nitrate was 65% after 6 hours, which enhanced with increasing N/S ration of influent. The result showed bacteria reduced nitrate to nitrite at first step, and resulted in accumulation of nitrite to 93 mg x L(-1) to the large extent. Accumulated nitrite was disappear on low influent N/S ratio condition after 6 hours, and need 21 hours on high influent N/S ratio condition. So, complete sulfide and nitrate removal was achieved during 6 hours. The results revealed that the sharp decreasing of sulfide concentration attributed to the reaction between sulfide and biosulfur particles to form polysulfide anions. In addition, biosulfur produced in 3 hours was the main source of electron donor for reducing nitrate.