The recent investigation indicates that the kinetic constants for anionic ions were merely the result of ion exchange between the algae cell wall surface and the anionic ion. In this study, Zygnema sterile and Lepocinclism textra, floating flagellate alga as the dominant algae strains, were cultivated using HRABR(High Rate Algae Biomass Reactor) and the cultivation conditions were 24 hrs. and 12 hrs. irradiation and it was studied how this algal biomass acts on the biosorption mechanism of anionic N and P. Results are as follows : 1. Calculating the specific chl.-a growth rate using Michaelis-Menten model, the one of 24hrs. irradiation was about 55 times higher than the one of 12 hrs. irradiation 2. Calculating the specific chl.-a growth rate using Kuo model, the one of 24 hrs. irradiation was about 2.26 times higher than the one of 12 hrs. irradiation 3. Langmuir model can apply to the biosorption mechanism of anionic N and P in HRABP. 4. Regarding the chlorophyll-a concentration as unit weight of sorbent, the ion selectivity coefficients for N and P are as follows : $(NH_3-N)+(NO_3-N)$ in 24 hrs. irradiation ; 44.984 $PO_4-P$ in 24 hrs. irradiation ; 24.237 $(NH_3-N)+(NO_3-N)$ in 12 hrs. irradiation ; 1432.851 $PO_4-P$ in 12 hrs. irradiation ; 599.076