This study evaluated the effect of different concentrations of vitamins, B₁₂ and C in the process of wastewater treatment by the blue – green algae Synechocystis aquatilis and Chroococcus schizodermaticus. C. schizodermaticus was more efficient than S. aquatilis in removing phosphorus by using both vitamins at all concentrations, while maximum nitrate removal was attained after 20 days using vitamin C at concentration 25 mg/l in case of C. schizodermaticus reactor. Vitamin B₁₂ caused the accumulation of nitrate in both algal reactors after 6 days at concentration 50 mg/l, while that accumulation began after 8 days with the use of concentration 75 mg/l. Concentration 25 mg/l of vitamin B₁₂ caused accumulation after 6 days in C. schizodermaticus reactor and after 12 days at S. aquatilis reactor. Ammonia was completely disappeared from wastewater treated by C. schizodermaticus using vitamin B₁₂ (concentration 75 mg/l) and vitamin C at its three concentrations in C. schizodermaticus reactors and only at concentration 25 mg/l in case of S. aquatilis reactor.