This study was designed to analyze the chemical composition of Citrus obovoides (Geumgamja) and Citrus natsudaidai (Cheonyahagyul) oils and to test their biological activities. These citrus essential oils were obtained by steam distillation of fruits collected from Jeju Island, Korea, and were analyzed using gas chromatograph (GC)-flame ionization detectors (FID) and GC-MS. Limonene and gamma-terpinene were the major components of the two citrus species. To evaluate in vitro anti-acne activity, they were tested against Propionibacterium acnes and Staphylococcus epidermidis, which are involved in acne. The Geumgamja and Cheonyahagyul oils exhibited antibacterial activity against both P. acnes and S. epidermidis. Their effects on DPPH radical scavenging, superoxide anion radical scavenging, and nitric oxide radical were also assessed. Cheonyahagyul and Geumgamja exhibited only superoxide anion radical-scavenging activity. To assess their potential usefulness in future cosmetic product applications, the cytotoxic effects of the two oils were determined by colorimetric MTT assays using two animal cell lines: normal human fibroblasts and HaCaT cells. They exhibited low cytotoxicity at 0.1 microl/ml in both cell lines. In addition, they reduced P. acnes-induced secretion of interleukin-8 (IL-8) and tumor necrosis factor alpha (TNF-alpha) in THP-1 cells, an indication of anti-inflammatory effects. Therefore, based on these results, we suggest that Geumgamja and Cheonyahagyul essential oils are attractive acne-mitigating candidates for topical application.