An effective analytical method of gas chromatography/mass spectrometry (GC/MS) was developed for the rapid determination of essential oils in the crude extract of Acorus species (Acorus gramineus, Acorus tatarinowii, and Acorus calamus). Major phenypropanoids (${eta}$,${alpha}$-asarone isomers, euasarone, and methyleugenol) and ${eta}$-caryophyllene in Acorus species were used as marker compounds and determined for the quality control of herbal medicines. To extract marker compounds, various extraction techniques such as solvent immersion, mechanical shaking, and sonication were compared, and the greatest efficiency was observed with sonication extraction using petroleum ether. The dynamic range of the GC/MS method depended on the specific analyte; acceptable quantification was obtained between 10 and 2000 ${mu}g/mL$ for ${eta}$-asarone, 10 and 500 ${mu}g/mL$ for ${alpha}$-asarone, 10 and 200 ${mu}g/mL$ for methyleugenol, and between 5 and 100 ${mu}g/mL$ for ${eta}$-caryophyllene. The method was deemed satisfactory by inter- and intra-day validation and exhibited both high accuracy and precision, with a relative standard deviation < 10%. Overall limits of detection were approximately 0.34-0.83 ${mu}g/mL$, with a standard deviation (${sigma}$)-to-calibration slope (s) ratio (${sigma}$/s) of 3. The limit of quantitation in our experiments was approximately 1.13-3.20 ${mu}g/mL$ at a ${sigma}$/s of 10. On the basement of method validation, 20 samples of Acorus species collected from markets in Korea were monitored for the quality control. In addition, principal component analysis (PCA) and hierarchical cluster analysis (HCA) were performed on the analytical data of 20 different Acorus species samples in order to classify samples that were collected from different regions.