In recent years,fruit juice adulteration has become an increasingly important issue.Rapid evaporative ionization tandem mass spectrometry(REIMS),as a novel method for real time discrimination of samples,could solve this problem without any sample preparation.In this paper,a metabolomics fingerprinting approach for real time authentication of orange,apple and grapefruit juices was developed.A discriminate model established by principal component analysis(PCA) and linear discriminate analysis(LDA) was able to distinguish different types of fruit juice with a correct classification of 9728% in leave 20% out cross validation and a 100% burns correctly identified in real time recognition.Characteristic m/z markers were detected and some of them were identified.Adulterated orange juices with apple and grape juices at different percentages could be well distinguished from the level of 50% down to 10%.Furthermore,the adulterated samples were analyzed by optimized single MS and tandem MS/MS REIMS(REIMS and REIMS/MS).Partial least squares analysis was successfully used to predict the level of the adulterants(both R2 and Q2>082 for all models).REIMS/MS could offer higher prediction accuracy compared with the conventional REIMS.