Kratom is the leaves of Mitragyna speciosa, which is native to Southeast Asia, and is increasingly used forrecreational and therapeutic purposes without medical supervision. Due to its indole alkaloid components, such as mitragynineand 7-hydroxymitragynine, it causes stimulating effects at low doses and opioid-like actions at high doses, and may exhibitvarious side effects that can lead to death when taken in an overdose and combined with other drugs, and thus it is consideredto be regulated. In this case, kratom was seized from a Thai man, and his urine was commissioned to confirm whether hewas taking kratom. Mitragynine, 7-hydroxymitragynine, 9-O-demethylmitragynine and 16-carboxymitragynine were detected inurine using liquid-liquid-extraction and LC-QTOF-MS.