This experiment was conducted in an aerated single-stage reactor at activated sludge concentration of about 3000 mg· dm-3. The influence of hydraulic retention time on nitrogen removal from rural wastewater was investigated. Hydraulic retention times were 24 and 12 hours. Two series were performed at a constant C/N ratio of 3.5. Enhancement of carbon removal from 83.8% to 87.6% was observed. An increase of activated sludge loading from 0.11g COD · g-1 · d-1 to 0.25 g COD · g-1 · d-1 did not cause total inhibition of nitrifica-tion, but nitrification efficiency decreased from 78.8% to 55.5%. Higher nitrogen removal efficiency (52%) was achieved in series I at 24 hours reaction time in contrast to shorter one (42%). Despite the fully aerobic condition, denitrification was observed. The denitrification process was pos-sible due to the use of accessibility of high amount of readily bioassimilable organic compounds. Obtained denitrification efficiency at C/N ratio 3.5 was about 50% during both experimental periods.