The objective of this study was to elucidate the chemical composition of essential oil from Cymbopogon nardus (citronella oil) and its antifungal activity. Chemical composition of the citronella oil was determined by capillary gas chromatography (GC) and GC/ mass spectrometry. Major constituents of the oil were geraniol (35.7% of total volatiles), trans-citral (22.7%), cis-citral (14.2%), geranyl acetate (9.7%), citronellal (5.8%) and citronellol (4.6%). The antifungal assay using the vapor-agar contact method showed that the crude essential oil markedly suppressed the growth of several species of Aspergillus, Penicillium and Eurotium at a dose of 250 mg/L in air. The most active compounds among the 16 examined volatiles, consisting of 6 major constituents of the essential oil and 10 other related monoterpenes were citronellal and linalool. Citronellal and linalool completely inhibited the growth of all tested fungal strains at a dose of 112 mg/L. Their minimum inhibitory doses ranged from 14 to 56 mg/L. The α- and β- pinenes showed an inhibitory activity against some fungi, whereas the other 8 volatile compounds lacked this property.