It takes a long time to measure the N mineralization potential by the incubation method. To shorten the incubation time, the incubation temperature was raised, and to measure simultaneously the C mineralization potential, headspace air in the incubation bottle was replaced by N2. That is, an anaerobic incubation method was proposed. Estimated amount of N mineralized in anaerobic incubation was in agreement with that in paddy incubation compared with that in upland incubation. Minimum incubation time, which was necessary to measure the rate constant accurately, was 18 days on the average, ranging from 8 to 43 days. Through anaerobic incubation at 40 ℃ , the incubation time was reduced to half of that at 35 ℃ . The N mineralization potential showed a positive correlation with the C mineralization potential in Brazilian upland soils.