Acid is added to a target sample such as urine, blood plasma or serum for converting mevalonic acid contained in the sample to lactone mevalonate, and the sample is irradiated with near infrared Raman excitation light, for determining mevalonic acid by measuring generated Raman scattered light. This method employs no mediatory reaction with simple pretreatment, requires no high-priced measuring apparatus, and can determine mevalonic acid in a short time.