L- histidine is one of the 20 amino acids that form proteins. The amino acid contains number of amino group which potentially play considerable role in N mineralization in soil. Nitrogen mineralization is a key process controlling productivity of natural ecosystems as well as agroecosystems. The sustainability of the ecosystems is greatly affected by the soil N processes and hence is of great importance. Environmental factors affecting the rate of N mineralization has been widely studied however, the effect of the type of organic molecules which possess N has not been adequately investigated. There are some similarities between L-histidine and L-arginine in terms of the molecular weight furthermore, it has been reported that inorganic N release following their incorporation to calcareous soils are pretty similar. Literature studies revealed that L-arginine ammonification has been widely measured in soils by a standard developed method and many researchers have pointed out that the process has a significant association with microbial biomass and activities. Therefore we raised this idea that L-histidine ammonification can similarly be used as an index of soil microbial activity and/or biomass in soil. In order to test the hypothesis, we encountered to a gap in the knowledge due to lack of a standard reliable method for measuring L-histidine ammonification in soils. There is a need to develop a reliable method to measure L-histidine ammonification accurately and precisely. Five surface soils (0-15 cm) were collected from major agricultural areas of Isfahan Province. Soils were mostly air-dried at the time of sampling. Two subsamples were prepared. An air-dried subsample was used for soil general characterization and a pretreatment was performed to the second subsample in order to build up soil microbial populations. Microbial biomass N was measured by fumigation-extraction method. To develop a standard method, the effects of substrate concentration, incubation temperature, incubation duration and shaking during incubation was examined. L-histidine was used at 0, 0.25, 0.5, 1.5, 2, 2.5, 5, 7.5 and 10 mg kg -1 . L-histidine ammonification was measured at four temperatures including 10, 20, 30, 40 °C. The process was evaluated at three incubation time including 3, 6 and 10 hours. Two shaking status was tested, without shaking and shaking with the rate of 150 rpm during incubation period. Our results indicated that the four investigated parameters have significantly influenced the rate of L-histidine ammonification in the calcareous soils. We figured out that the optimum substrate concentration, temperature, duration were 0.5 mg kg -1 , 30°C, 10 hours respectively, when they have been applied without shaking. We reexamined the developed method in plant-residue treated soils and found out that when wheat and alfalfa root added to the soils, the method worked. The only caution was that higher substrate concentration (2 mg kg -1 ) was needed. It was noteworthy that application of the plant residues to the soils significantly enhanced soil basal respiration, substrate induced respiration and L-histine ammonification proportionally whereas, highly significant correlations were observed among the parameters.This finding shed light on our hypothesis suggesting that L-histidine can be probably used as another index of soil microbial activity and/or biomass. The range of thermodynamic values including temperature response (Q 10 ) and activation energy (E a ) were calculated and showed that the method developed here is sensitive enough to detect the differences between thermodynamic parameters among soils and plant residue treatments. Overall, we welcome the new method developed and suggest that the method needs to be evaluated and calibrated in a wide range of soil types and treatments. It has the potential to be a soil quality assessment index when being considered along with other biological measurements.