In this study, the optimal ratio of nitrate to phosphate in the lab scale phytoremediation by two species of Pampas Grass and Bamboo Vtlndy using synthetic sewage was determined. After initial experiments, optimal retention time of 8 days was determined and on this basis, the study was continued. All results at each stage were examined using T-test analysis. The results showed that in the maximum error of 5%, maximum removal of 84.45 and 54.33 percent in Pampas Grass and bamboo were occurred in nitrate to phosphate ratio of 50:50 and 25:25, respectively while the total amount of pollutants were removed in the ratio of 100:100 and the rate of 2.67 and 1.82 gr/kg based on dry weight, respectively using Pampas Grass and bamboo. The results showed that in the range of 5 percent error level, the rate of removal and absorption of Pampas Grass was higher than bamboo.