Land use change can influence the content and balance of nutrients in soil. The mineralization and immobilization of N by microorganisms are central processes in terrestrial N cycling. Both inorganic and organic N are involved in these processes. Inorganic N ( NH 4 + and NO 3 - ) has been analyzed more frequently, while, structurally complex organic N molecules represent the largest soil N pool ( 95%). Soluble organic N can be as mobile as nitrate and can be considered as a considerable source of in situ production of inorganic N in higher soil depths. Moreover, recent evidences have shown that some organic molecules like amino acids can be directly taken up by plant roots. This study examined the effect of land use change on soil soluble organic N( SON), inorganic N and amino acids pools in three forest ecosystems. Sites were selected to represent the variable climatic conditions of main forest regions of Iran. Soil samples were collected from a humid region in western Guilan (Gisum forest), in mountainous regions of Mazandaran (Roudbarak forest) and semi-arid regions of Chaharmahal-va- Bakhtiari (Delvara forest). The soil samples were taken from three depths in Roudbarak and Gisum forests ( 0- 20, 20- 40 and 40- 60 cm) and one depth in Delvara forest( 0- 15 cm). All measurements were performed in three replications. Changes in SON, IN and soil amino acids pools during a 22 weeks of incubation at 25°C and 50% water holding capacity were monitored. The experiment was a factorial combination of factors in a completely randomized design (CRD) with 2 factors( land use and depths or tree species and depths). Average concentrations of inorganic N ranged from 28 to 180 mg kg -1 N, 21 to 178 mg kg -1 N and 30 to 181 mg kg -1 N at Roudbarak forest, Gisum forest and Delvara forest, respectively. Average SON concentrations ranged from 23 to 380 mg kg -1 N, 21 to 444 mg kg -1 N and 21 to 441 mg kg -1 N at Roudbarak forest, Gisum forest and Delvara forest, respectively. Average soil amino acids concentrations ranged from 0.090 to 2.7 mmol kg -1 , 0.043 to 4.7 mmol kg -1 and 0.017 to 1.3 mmol kg -1 at Roudbarak forest, Gisum forest and Delvara forest, respectively. Ratio of SON to inorganic N was 2.43 and 3.61 in 0- 20 and 20- 40 cm at Roudbarak forest respectively, 1.94 and 4.58 in 0- 20 and 20- 40 cm at Gisum forest, respectively. The ratio wa 2.37 in 0- 15 cm at Delvara forest. The results of discriminant analysis showed that the first depth( 0-20 cm) consisted a distinctive community and other depths( 20- 40 and 40- 60 cm) were combined. . The concentrations of SON, inorganic N and soil amino acids were decreased with depths. Distinctive differences were observed between surface and subsurface depths. Land use