The genus Microsorum is composed of about 40 species mainly distributed in the tropical area of Asia. In China, there are 9 species [1]. Phytochemical studies on plants of the Microsorum genus have yielded various types of compounds such as triterpenoids, sesquiterpenoids, flavonoids, lignan, uracil, uridine, sterols, and volatiles [2–7]. M. insigne Copel. has been grown in southern China and other countries in southeastern Asia and is used in traditional Chinese medicine to treat arthralgia, traumatic injury, cut wound, and hemorrhage [8]. It has also been used as a popular and healthful vegetable in Yunnan of southwestern China. Previously there has been no report on its chemical constituents. We report here the results of our studies on the composition of the essential oil from the dried aerial parts of M. insigne. The fresh aerial parts of M. insigne Copel. were collected from Pingbian, Yunnan of China and identified by Mr. Liang-Chao Qian, a botanist from the National Natural Reserve in Dawei Mountain, Pingbian, Yunnan of China. A voucher specimen is kept in the Herbarium of the Department of Chemistry, Yunnan Normal University, Kunming, China (No. 09051501). The dried aerial part was crumbled and hydrodistilled for 5 hours using a Clevenger apparatus. The yield of yellowish oil was 0.0175% (w/w). The oil was subsequently dried over anhydrous sodium sulfate and stored at 4 C until analysis. The essential oil was subjected to gas chromatographic/mass spectral analysis using an Angilent 6890 GC with an Agilent 5973 mass selective detector. The analytical conditions included an HP-5MS (30 m 0.25 mm 0.25 m) quartz capillary chromatography column; carrier gas: helium with flow rate 1.0 mL/min; volume injected: 1.0 L; split ratio: 15:1; 80 C thermostat temperature programmed at 5 C/min to 260 C, and 230 C detector and vaporizer temperature. Constituents of the oil were identified by comparing the mass spectra of the products with data in the Wiley7N.L mass-spectra library. The identified components and their percentages are given in Table 1, where the components are listed in the order of their elution on the column. Forty-four components were detected in the oil, representing 92.1% of the total oil. As can be seen, the major components of the oil are n-hexadecanoic acid (31.9%) and N-(2-phenethyl)-3-chloropropionamide (15.9%). The aliphatics (46.5%) were the dominant group in the oil. The aromatic compounds (31.8%) were the second, whereas terpenes (monoterpenes, 8.6%; sesquiterpenes, 2.6%; diterpenes, 1.9%) accounted for 13.1%. It is interesting that 23.6% of nitrogencontaining compounds were found in the oil, among which the anticonvulsant chlorinated molecule N-(2-phenethyl)-3chloropropionamide accounted for 15.9% [9].