Abstract: OBJECTIVE To study the tissues distribution characteristics of stachyose in rats after pulmonary delivery of micronized Rehmanniae Radix oligosaccharide (RGOS). METHODS A single dose of 100 mg·kg^-1 micronized RGOS was given to healthy SD male rats via pulmonary administration. The tissues of liver, kidney and lung were acquired at 0.25, 0.5, 1, 3, 5, 8 and 12 h after administration. The concentrations of stachyose in tissue samples were determined by LC-MS/MS on an Asahipak NH₂P-50 4E column(250 mm×4.6 mm, 5 μm) with an Asahipak NH₂P-50G 4A guard column (10 mm×4.6 mm), and the column temperature was kept at 25℃ The mobile phase consisted of acetonitrile and water (55:45) at a flow rate of 1 mL·min^-1. The auto-sampler was conditioned at 4℃ and the sample injection volume was 1 μL. Detection and quantification were conducted by LC-MS/MS method in the negative ion mode using multiple reaction monitoring (MRM) transitions at m/zM-H^- 665.4→383.1 for stachyose and 665.5→485.0 for IS, respectively. RESULTS After pulmonary administration of 100 mg·kg^-1 micronized RGOS in rats, stachyose was mainly distributed in kidney. The concentrations of stachyose in liver was low. The concentrations of the tissues at 15 min after pulmonary administration all reached the highest, in which the liver occupied (43.20±5.60)μg·mL^-1, kidney occupied (130.80±7.01)μg·mL^-1 and lung (1 112.00±98.54)μg·mL^-1, then the concentrations decreased gradually, but the concentration of stachyose in kidney tissue increased after 5 h and then decreased continually. CONCLUSION The in vivo eliminatiion of stachyose is fast. The present investigation on stachyose tissues distribution can provide information for the further study and clinic use of micronized RGOS.