The objective of this research was to compare the effectiveness of water hyacinth and cootail for wastewater treatment by taking water sample from Klong Bangkhen-mai near King Mongkut’s University of Technology North Bangkok. The results showed that there was no diifference on water temperature changes in tanks between two plants. pH of water in coontail tanks was between pH 8.69 to pH 8.91 and pH of water in water hyacinth tanks was slightly increasing between pH 7.71 to pH 8.26. The more amount of coontail added the higher DO would be between 9.18 mg/L to 10.02 mg/L. Moreover COD of water was decreasing according to the amount of cootail addition and more effective than that in water hyacinth tank especially in 150 grams coontail tanks but TS in water hyacinth tanks was much more decreasing than that in coontail tanks. TS was between 21.73 mg/L to 25.91 mg/L. COD was between 45.30 mg/L to 48.34 mg/L.