本文报道了熏蒸法测定红壤微生物量氮的研究结果。用扩散法与经典的蒸馏法测定浸出液中全氮量，两法之间有较好的一致性（ｒ＝０９９３），差异不显著，而扩散法更适用于大批样品的分析。经对红壤固定铵能力的测定，显示红壤对铵的固定不明显，不影响红壤微生物量氮的测定，故无须进行铵固定的校正。１１个红壤土样的微生物量Ｎ为１０７７～３１６７ｍｇ／ｋｇ，微生物量的Ｃ／Ｎ变化范围为４１～１２６，平均６７。 This paper reports the results of fumigation method for the determination of microbial biomass nitrogen in red soil. Diffusion method and classical distillation method to determine the amount of total nitrogen in the leachate, there is a good agreement between the two methods (r = 0993), the difference is not significant, but the diffusion method is more suitable for a large number of samples. The determination of immobilized ammonium in red soil showed that immobilization of ammonium in red soil was not obvious and did not affect the determination of microbial biomass nitrogen in red soil. The microbial biomass N in 11 red soil samples ranged from 1077 to 3167 mg / kg, and the microbial biomass C / N ranged from 41 to 126 with an average of 67.