Volatile components of the essential oils of Satsuma mandarin (C. unshiu), Dangyuza (C. grandis), Yuza (C. junos), Byungkyul (C. playtymamma), Jinkyul (C. sunki), and Hakyul (C. natsudaidai) grown in Jeju Island were isolated from the fruit peels by hydro distillation and determined by GC-MS. GC-MS analysis identified 58 compounds, with main components being d-limonene $(64.01{sim}79.34%),;{eta}-myrcene;(3.01{sim}26.53%),;{gamma}-terpinene;(0.11{sim}12.88%),;{eta}-pinene;(0.78{sim}4.74%),;and;{alpha}-pinene;(1.01{sim}2.55%)$. Differences in compositions and contents of the essential oils were observed among citrus varieties. Effects of citrus oils on growth inhibitions of Escherchia coli, Staphyllococcus epidermidis, and Candida albicans were investigated using disc diffusion assay and minimal inhibitory concentration (MIC) assay. The essential oils inhibited growths of the test organisms, exhibiting higher levels of activity against Gram-positive S. epidermidis (MIC values $0.04{sim}0.17mg/mL$), whereas Gram-negative E. coli was moderately resistant (MIC values $1.66{sim}20.30mg/mL$). MIC of citrus essential oils ranged from $0.82{sim}23.69mg/mL$ against C. albicans. The essential oils obtained from C. sunki, C. grandis, and C. playtymamma showed the highest antimicrobial activities against S. epidermidis and C. albicans, indicating their potential as natural antimicrobial agents.