Abstract: Essential oils from the fresh rhizomes and the naturally aged rhizomes of Iris pallida Lam. were analyed by GC-MS, respctively, and the relative contents of constituents were determined by area normalization method. The antimicrobial activity of the essential oil was evaluated against 3 fungi and 12 bacteria including 7 clinical isolated strains. The results show that: twenty-six volatile components were identified and determined in the oil of the fresh rhizomes, accounting for 92.09%of the total area of the peak, and the main compounds of the oil were tetradecanoic acid (31.77%), hexanoic acid(15.33%), 3-methyl-butanoic acid(12.20%), pentanoic acid(9.29%), heptanoic acid(7.91%), 3-methyl pentanoic acid(7.25%),octanoic acid(2.44%),2',4'-dihydroxy-3'-methylacetophenone(1.04%). Forty-five volatile components were identified and determined in the oil of the naturally aged rhizomes, accounting for 85.63% of the total area of the peak, and the main compounds of the oil were tetradecanoic acid(28.02%), tetradecanoic acid, ethyl ester(10.42%), 9,12-octadecadienoic acid(7.67%), dodecanoic acid(6.41%), hexanoic acid(5.14%), hexadecanoic acid(4.44%), dodecanoic acid ethyl ester(4.09%), linoleic acid ethyl ester(3.87%), hexadecanoic acid ethyl ester(3.13%), ethyl oleate(2.85%), α-ionone, 6-methyl-(1.39%), and decanoic acid(1.31%); the oil of the fresh rhizomes presented a broad antimicrobial spectrum, and the minimal inhibitory concentration (MIC) value was 0.25g/Land the minimal bactericidal concentration (MBC) value was 0.35g/L; the oil of the naturally aged rhizomes presented a broad antimicrobial spectrum, and had better antimicrobial activity against gram-positive bacteria, MIC value was 0.05g/L and MBC value was0.08g/L.

Key words: Iris pallida Lam., essential oil, antimicrobial activity