OBJECTIVE： To establish a method for the simultaneous concentration determination of saxagliptin and its metabolite 5-hydroxy saxagliptin in diabetic model rats in vivo. METHODS： UPLC-MS/MS was performed on the column of Waters BEH Shield RP18 with mobile phase of 10 mmol/L ammonium acetate-acetonitrile （70 ∶ 30， V/V） at a flow rate of 0.3 mL/min， column temperature was 30 ℃， and injection volume was 10 μL. Scanning mode was multi-reactive monitoring with positive ion mode， and each ion pair was m/z 316.2→180.2 （saxagliptin）， m/z 332.3→196.2 （5-hydroxy saxagliptin） and m/z 304.2→153.9 （vildagliptin， internal standard）. 6 SD rats were selected and intragastric administred saxagliptin 0.53 mg/kg after inducing diabetic models. Blood sample 0.25 mL was taken from eyes before administration and after 0.25， 0.5， 0.75， 1.0， 1.5， 2.0， 4.0， 6.0， 8.0， 12.0， 24.0 h of administration. Plasma concentration of saxagliptin and its metabolite 5-hydroxy saxagliptin were determined， and Win Nonlin 6.1 software was used to calculate the pharmacokinetic parameters. RESULTS： The mass concentration of saxagliptin and 5-hydroxy saxagliptin ranged in 0.1-100， 0.2-200 ng/mL（r＝0.997 2， 0.996 5）； limits of quantitation were 0.1， 0.2 ng/mL； inter-day and intra-day RSDs were less than 12％ （n＝5， 3）； accuracy was 94.1％-105.4％， 91.0％-103.6％； extraction recoveries were 72.4％- 87.3％， 107.0％-115.3％ （RSD＜13.6％， n＝6）； matrix effects were 105.9％-107.8％， 83.5％-88.2％ （RSD＜10.3％， n＝6）；RSD of stability was less than 11.0％（n＝5）， respectively； and pharmacokinetic parameters as cmax were （49.97±11.14）， （16.87±7.35） ng/mL， t1/2 were （2.88±0.21）， （4.21±0.95） h， AUC0-24 h were （90.95±7.06）， （49.13±5.33） ng·h/mL （n＝6）. CONCLUSIONS： The method is simple， accurate， specific， and suitable for the pharmacokinetics research of saxagliptin and its metabolite 5-hydroxy saxagliptin in diabetic rats in vivo.