OBJECTIVE：To investigate th e stabilities of antitumor candid ate Gedatolisib in plasma in vitro and simulated gastric/intestinal fluids ，and to analyze the possible catabolites in plasma. METHODS ：HPLC method was adopted. Using indometacin as internal standard ，the contents of Gedatolisib incubated in plasma of SD rats （male）for 0，0.5，1.0，1.5，2.0，3.0 h and blank simulated gastric fluid （pH 1.3，no enzyme ），blank simulated intestinal fluid （pH 6.8，no enzyme ），simulated gastric fluid（pH 1.3，containing pepsin ）and simulated intestinal fluid （pH 6.8，containing trypsin ）for 0，0.5，1.0，2.0，3.0，4.0，6.0 h were determined. The remaining percentage of Gedatolisib was calculated. UPLC-Q-TOF/MS was used to analyze the TIC of blank plasma and incubated samples. The differential peaks were compared， and catabolites were inferred by MS 1Z073）.gzwjkj2019-1- chromatograms. RESULTS ： The remaining percentage in plasma of rats for 2.0 h was about 63％，and there was nosignificant change after continued incubation. The remaining percentage of Gedatolisib incubated in blank simulated intestinal fluid for different time ranged （99.18 ± 2.15）％ -（103.20 ± 3.41）％ . The remaining percentage in simulated com intestinal fluids for 2.0 h ranged （88.76 ± 1.53）％ . The remaining percentage in blank simulated gastric fluids for 2.0 h was ranged （85.63±1.55）％，and there was no significant change after continued incubation. The remaining percentage in simulated gastric fluid was from （94.94±3.52）％（0 h）to（16.19±1.17）％ （6.0 h）. TIC of UPLC-Q-TOF/MS showed that the differential peaks of incubated samples and blank plasma was 6.42 min under positive mode scanning ，molecular ion peak of m/z 616.335 1，simulated 632.327 7，630.317 0，602.278 6 [M+H]+ could be found in scanning channel. It was speculated that Gedatolisib could generate 1-（4-（3-（4，6-dimorpholino-1，3，5-triazin-2-yl）phenyl）urea） benzoyl）-N，N-dimethylpiperidin-4-amine oxide ，1-（4-（4-（dimethylamino）piperidine-1-carbonyl）phenyl）-3-（4-（4-morpholino-6- （3-oxomorpholino）-1，3，5-triazin-2-yl）phenyl）urea and 1-（4-（3-（4-（4，6-dimorpholino-1，3，5-triazin-2-yl）phenyl）urea） benzoyl）-N-methylpiperidine. CONCLUSIONS ：Gedatolisib is not stable in rat plasma ，and it may undergo terminal N oxidation， morpholine ring oxidation and terminal N demethylation. Gedatolisib is stable in artificial intestinal fluid and blank artificial gastric/ intestinal fluid ，and degrades obviously in the presence of pepsin.