Inhibition of ammonia oxidation and nitrite oxidation was studied in an immobilized biomass system. Ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) suffered different inhibition in ammonia-rich wastewater. NOB started to be inhibited when FA (free ammonia) was 2mg/L, and was totally inhibited when FA was 8mg/L. AOB started to be inhibited when FA was 22mg/L, and tended to lose activity when FA was higher than 170mg/L. Inhibition kinetics of ammonia oxidation and nitrite oxidation could be described by Haldane model. Immobilization alleviated inhibition of FA to nitrifiers, maintaining high activity even at high strength ammonia solution. Partial nitrification could be achieved by varying degrees of inhibition of FA to AOB and NOB.