According to traditional usage, the extract of Longan Arillus was tested for its anxiolytic-like effect by application of the Vogel-type anti-conflict method in mice. The extract indicated significant activity at a dose of 2 g/kg, s.c., and results of the bioassay-oriented isolation revealed adenosine to be the active principle. Adenosine produced the anti-conflict effect significantly at a dose of 30 mg/kg, s.c. Adenine, uridine, and 5-methyluridine did not exhibit the effect, although these compounds were isolated from the extract. Some other related compounds such as AMP and c-AMP showed no effect, except for inosine. Adenosine also contributed to the analgesic effect which was observed in the extract by the writhing method.