Analytical method for synephrine and octopamine in citrus fruits, drinks containing citrus fruit, and human urine was developed using gas chromatography / mass spectrometry(GC/MS). Silylation with MSTFA, acetylation with MBTFA, and trimethylailylation with MSTFA followed by tritluoroacetylation with MBTFA were compared. The selective derivatization of aynephrine and octopamine was optimized with two derivatizing reagents ; MSTFA and MBTFA. The ion at mlz 267 was monitored to characterize the benzyl group of the both compounds. Synephrine was detected in the concentrations of 0.46-1.88 ug/g for citrus fruits and 1.2-8.1 ug/ml for drinks. The urinary excretion data of aynephrine showed the highest concentration at the period of 8-20 hours after drinking orange juices and total amounts of its urinary excretion calculated as a parent compound was 11-14% of a dose during 48 hours. Octopamine was not detected in citrus fruits, drinks, and human urine.