This experiment was conducted in a bioreactor with biomass immobilized in ceramic carriers. The influence of hydraulic retention time (HRT), carrier structure and intrinsic circulation rate on carbon and nitrogen removal from municipal wastewater were investigated. Two types of ceramic carriers were used at HRT 70, 60, 40, 30 min for carrier I, and 70, 60, 30, 15 min for carrier II, and at the circulation rate of 60, 40 and 20 dm3·h-1. The highest nitrogen removal efficiency was achieved in carrier II at 30 min of reaction. The carbon removal efficiency was similar for both carriers. An increase in internal circulation rate from 20 to 60 dm3·h-1 enhanced nitrogen removal efficiency from 33.0 to 47.2% and decreased in the production of surplus sludge in carrier II.