Abstract: Microalgae Nannochloropsis oculata, immobilized with sodium alginate, was used to explore its removal efficiency of NH4+-N and PO43--P from artificial sewage water. Algae ball size, cell densities, dosages of algae balls, and aeration cultured were applied in the single-factor. The results showed that all these conditions significant impact the removal of of NH4+-N and PO43--P. The growth rate of K value achieved the highest value (0.3320.002) when the diameter was 3.5 mm; the removal rate of NH4+-N and PO43--P were the highest one at the diameter was 3.5 mm, which were (75.083.83)% and (80.803.81)%, respectively. The maximum of the growth K values was (0.3300.033) with the density of 100104 cells/ball. The highest NH4+-N and PO43--P removal rate were (87.200.43)% and (82.581.72)%, respectively, at the group of 300104 cells/ball; however, 100104 cells/ball was the optimal algal cell density based on unit algal cells removal ratio of NH4+-N and PO43--P. The increased algae balls dosages decreased the growth rate of K values. 10 g/L group had the maximum K values (0.3010.02) and 50 g/L had the minimum K values (0.1930.01). The removal rates of NH4+-N were (84.120.78)% and (84.630.45)% when the dosage was 30 g/L and 50 g/L, respectively. 30 g/L group had the highest PO43--P removal rate (77.131.43)%. Combined analyses revealed that 30 g/L was optimum for the dosages of algae balls. The K value, the removal of NH4+-N and PO43--P were significantly (P0.05) higher with aeration than non-aerated; K values were (0.3060.006) and (0.1770.010), respectively; NH4+-N removal rates were (85.930.45)% and (49.320.45)%, respectively; PO43--P removal rates were (66.665.00)% and (46.292.12)%, respectively. This study optimized the conditions of immobilized microalgae Nannochloropsis oculata:immobilized Nannochloropsis oculata should be aerated cultures; algae ball size was 3.5 mm; the algal cell density was 100104 cells/ball; and the dosage of algae balls was 30 g/L.