Abstract: An enclosed intermittent vent method was used to measure the Ammonia(NH3) volatilization from a paddy soil of double-harvest rice system under different application amounts of urea. The results show that the NH3-N volatilization (NV) loss occurs mainly within 15 days, and the peak occurs during 3-5 days after the fertilization in the early rice season, and in the late rice season the NV loss occurs mainly within 11 days, and the peak appears in the third days after the fertilization. The total NV losses vary from 22.60～162.0kg N /hm2 and 22.35～141.4 kg N/hm2 in the early and late rice seasons, respectively, and the percents of the losses to the applied N amounts range from 29.29%～52.32% and 35.75%～46.82%, respectively. The total NV losses and their percentages in all of the early rice, late rice or the double-harvest seasons are linearly increased with the increase of the urea application rates.