Background: In the recent decade, artificial drying has been one of the most important needs of the pharmaceutical industries. In addition, different drying methods have different effects on the quantity and quality of the essential oils produced from medicinal plants.

Objective: The main objective of this study was to evaluate the effects of different drying methods (shade and oven drying at 35 °^C and 55 °^C) in comparison with the fresh sample on the essential oil yield and volatile composition of M. officinalis.

Methods: This experiment was conducted in completely randomized design with three replicates. The essential oil samples were isolated by hydrodistillation in a Clevenger type apparatus and analyzed using GC and GC–MS methods.

Results: Different drying treatments had a significant effect on the content of M. officinalis essential oil (ranging from 0.08 to 0.3 % v/w; overall average of 0.22% v/w). The main components of the essential oil of shade dried, oven-dried at 35 °C and oven-dried at 55 °C samples were β-caryophyllene, geranial and γ-cadinene, respectively. Oven drying at 55°C resulted in disappearance of neral, geranial and neryl acetate. Sesquiterpene hydrocarbons constituted the principal fraction of all samples, followed by oxygenated monoterpenes, except the oil of oven dried sample at 55°C in which oxygenated sesquiterpene represented as the second main fraction.

Conclusion: The highest essential oil yield was obtained from oven drying at 35°C which conserves the characteristic aroma of the spice, so this method seems to be more advisable for drying of M. officinalis.