To achieve sensitive detection of catecholamines in trace rat brain microdialysate samples,using d0/d3-10-methyl-acridone-2-sulfonyl chloride（d0/d3-MASC) as isotope-coded derivatization, a novel ultra high performance liquid chromatography-tandem mass spectrometry（UHPLC-MS/MS) method was developed for the detection of dopamine（DA),norepinephrine（NE) and epinephrine（EP) by ultrasonic-assisted dispersive liquid-liquid microextraction（UA-DLLME).d0-MASC（light form) and d3-MASC（heavy form) were used as derivatization reagents for microdialysate samples and standards,respectively.The mixture of two solutions was enriched by dispersive liquid-liquid microextraction,and 3 catecholamines were detected by UHPLC-MS/MS with heavy derivatives as internal standards for corresponding light derivatives.The result indicated that the stable derivatives were obtained in pH 10.8 buffer/acetonitrile at 37 ℃ for 3.0 min,and then were separated within 3.0 min.Linearity ranges were obtained in the range of 0.02-10.0 nmol/L（r>0.995) for three catecholamines, with LODs of 0.005-0.010 nmol/L and LOQs of 0.018-0.040 nmol/L.Compared with the reported methods,the method is a convenient and validated method for the sensitive and accurate determination of catecholamines in trace rat brain microdialysates.