A 26-year-old woman Japanese public official servant in Lao People's Democratic Republic was introduced to our hospital on December 12, 2002, because of two months duration of low grade fever and severe eosinophilia. There was no significant finding in physical examination. Laboratory tests showed leukocytosis (15, 700/μl) with severe eosinophilia (42%), and no abnormal lymphocyte was observed. Furthermore, elevation in alkaline phosphatase (748IU/l), gamma-glutamyl transpeptidase (190IU/l), leucine aminopeptidase (150IU/l), and slight elevation in CRP (2.8mg/dml) were pointed out. A computed tomographic scan of the abdomen obtained multiple cystic lesions in the right lobe of the liver. On parasitological study, a stool specimen examined by the formalin-ether concentration method revealed positive for Opisthorchis viverrini eggs. She was orally administered with40mg/kg of praziquantel a day for two consecutive days. Following check-up by medical-affairs official at Embassy of Japan in Lao PDR confirmed the normal eosinophil count and her fever disappeared. It was considered eosinophilia in this case was induced by acute phase of severe ophisthorchiasis.