In this study, high fat diet was fed to rats and the amount of vemurafenib in rat plasma was determined by the developed liquid chromatography with tandem mass spectrometry. The calibration curve was linear between 0.01 and 0.8 µg mL−1 vemurafenib with 0.999 regression coefficient. The limit of detection and quantification of the method are estimated from the signal to noise ratio 3:1 and 10:1, respectively. These are 1.10-4 µg mL−1 for LOD and 4. 10-4 µg mL−1 for LOQ. This method has been found to be reproducible and highly sensitive and provides a combination of faster analysis time and improved limits of detection.