The ability to measure plant hormones quantitatively is important as plant hormones regulate plant growth, development and response to biotic and abiotic cues. In this protocol, we describe the quantitative analysis of major plant hormones from crude plant extracts. Plant hormones are determined using reverse-phase liquid chromatography-tandem mass spectrometry with multiple reaction monitoring. The method provides quantification of most major plant hormones in a single run from 50 mg of fresh plant tissue. Extraction and quantitative analysis of 40 samples takes 2-3 d.