The various species of mint are used in different industries such as pharmaceutical, food, cosmetics and health industry. Mentha aquatica L. are important species of mint. Drying process, in order to maintain the quality and quantity of essential oil extraction of the plant, it has an important role in the processing medicinal plants. Dryer tests were conducted in June 2016. In this research, the effect of drying temperature and air velocity on the essential oil content of mint was studied. The drying test was performed in three air temperatures 40, 50 and 60°C, and two drying air velocity 1 and 2 m/s. The essential oils from each organ type were extracted by hydrodistillation and the chemical components were analyzed by GC-MS. The results showed that increasing the drying temperature of 40 to 60°C was caused the loss of compounds such as α-terpinene, piperitone and β-myrcene. In addition with increasing air velocity dryer of 1 to 2 m/s caused increasing the percentage of volatile compounds such as α-pinene, 1,8-cineole, β-pinene and menthol. According to results, menthol content decreased with an increase in the drying air temperature from 40 to 50°C and then increased as the drying air temperature increased to 60°C. Menthol content increased with an increase in the drying air velocity. The results of essential oil analysis showed that among all determined compounds: menthol (61.1%), menthyl acetate (15.1%), 1,8-cineole (9.8%) and menthofuran (8.6%).