Experiments were carried out to evaluate effects of initial stocking density of Spirulina platensis and supplementary Bacillus subtilis into wastewater catfish pond on growth of the algal population. In the first experiment, S. platensis were inoculated with different densities of 20x103; 30x103 and 40x103 cells/mL, respectively without bacteria supplement. The second experiment included four treatments with an addition of B. subtilis in densities of 105; 106, 107 CFU/mL, respectively and no supplement bacteria as control treatment; S. platensis was kept the same of 40x103 cells/mL. The highest algal density was 176±0.6 x 103 cells/mL to be obtained on the day-19 sine inoculation of 40x103 cells/mL treatment and significantly different from the other treatments (pB. subtilis supplement at 105 CFU/ml into wastewater of catfish pond was given the best result and different significant from the other treatments.