Abstract: In this study, we explored the ability to remove nitrate and phosphorus of two strains of Stigeoclonium spp. (SHY-370 and HB1617) by setting different initial concentrations of ammonia nitrogen and nitrogen/ phosphorus (N/P) ratios in synthetic wastewater. The results indicated that different initial concentrations of ammonia nitrogen in synthetic wastewater could affect the biomass concentration and the ability to remove N and P of SHY-370 and HB1617. The maximum ammonia nitrogen concentration in synthetic wastewater that SHY-370 can tolerate was 10 mg/L, while that was 5 mg/L for HB1617. The ammonia-nitrogen removal rate of SHY-370 and HB1617 was above 97% and the maximum daily ammonia-nitrogen removal rate was 3.98 mg/L/d, while the initial concentration of ammonia nitrogen in synthetic wastewater varied between 1-10 mg/L. N/P ratios had a slight impact on the biomass concentration of the SHY-370, however, the biomass concentration of HB1617 was reduced when the corresponding rate was over 20 mg/L. The concentration of total phosphorus (TP) in synthetic wastewater was 10 mg/L. When the N/P ratio was 2, the content of TP in synthetic wastewater was higher than 10 mg/L, which led to a low TP removal rate. According to the results of our study, we can conclude that SHY-370 and HB1617 are appropriate for the treatment of urban sewage in which the concentration of ammonia nitrogen is relatively low, whereas the concentration of TP and NO₃-N is relatively high.