In this study, we investigated the level of gut absorption following oral beclomethasone dipropionate (BDP) administration by measuring the blood concentration of its metabolites measured by LC-MS/MS using the HPLC method. Five patients who were administered BDP orally for gut GVHD were included. The blood concentrations of beclomethasone-17-monopropionate (17BMP), which is one of the active metabolites of BDP, were 618 approximately 1, 749 pg/mL in 4 of the studied 5 patients, which was comparable to that after inhalation of BDP; however, it was relatively higher in one patient (2,439+/-161 pg/mL). As the blood concentration of 17BMP in this study patient was higher compared with healthy volunteers administered a single oral BDP 4 mg, GVHD patients might have a higher concentration than healthy volunteers. Given that a higher grade of gut GVHD was associated with a higher blood level of 17BMP, BDP absorption might be associated with gut mucosal injury. Thus, the systemic adverse effect following oral BDP administration might not be negligible especially in gut GVHD patients.