Furocoumarins, produced by some plants as a defense mechanism against predators, are known in some cases to cause photosensitization or interact with medications in humans. The aim of this study was quantitative determination of furocoumarin and coumarin levels in 23 samples of essential oils and 8 samples of yuzu seed oils. Gas and liquid chromatography-mass spectrometry and high-performance liquid chromatography were performed to measure the concentrations of angelicin, trioxsalen, 6′,7′-dihydroxybergamottin, bergamottin, osthol, psoralen, xanthotoxin, bergapten, isopimpinellin, and auraptene in the oils using 4-chlorobenzophenone as an internal standard. Angelicin was detected only in angelica (Angelica archangelica) at a concentration of 72.5 mg/kg, along with osthol at a high concentration of 730 mg/kg. A small amount of trioxsalen was detected in juniper (Juniperus communis) , litsea cubeba (Litsea cubeba) , lemongrass (Cymbopogon flexuosus) , and lemon verbena (Lippia citriodora) oils. 6′,7′-Dihydroxybergamottin was found in grapefruit (Citrus paradisi) peel oil at concentrations up to 300 mg/kg. Bergamottin was present in oils from some plants belonging to Rutaceae and Apiaceae families, with the highest concentration of up to 3,550 mg/kg in bergamot (Citrus bergamia) oil. Furocoumarins and coumarins were either absent or found only in trace amounts in the commercial yuzu (Citrus junos) seed oils, although bergapten and xanthotoxin were detected in a crude laboratory-prepared yuzu seed oil at concentrations of 10.3 and 195 mg/kg, respectively. It was demonstrated that furocoumarins and coumarins were detected in several samples of essential oils and crude yuzu seed oils by the present method.