the comminution and distillation time are two important factors, which affect the essential oil yield and/or composition of aromatic plants significantly. to find out the suitable comminution process and optimum distillation time for isolation of essential oil from acorus calamus l., an experiment was conducted. the comminuted rhizomes (sliced and powdered) were hydrodistilled for different durations and their yields and compositions were compared. distillation of uncomminuted rhizome for 8 hours gave 2.37% of essential oil. however, in comminuted rhizomes, yield varied from 2.27 to 6.60% under different distillation durations. the resulting essential oils were analyzed using gc-fid and gc-ms. twenty-seven constituents, representing 94.7-97.2% of the total oil compositions were identified. major constituents of the oils were (z)-asarone (84.8-91.2%), and (e)-asarone (2.5-5.2%). the comminution and distillation time showed noteworthy effect on the essential oil yield; however, they showed no major change on the essential oil composition of a. calamus. it was concluded that powdering of dried rhizomes and effecting distillation for 4 hours are appropriate parameters for extracting maximum essential oil from a. calamus at laboratory scale.