The present invention provides a mass spectrometry method that can achieve analysis with high sensitivity using a matrix additive capable of improving ionization efficiency in mass spectrometry. A mass spectrometry method comprising the steps of: forming a mixed crystal for mass spectrometry on a target plate for mass spectrometry, the mixed crystal comprising a sample to be analyzed, a matrix, and a matrix additive selected from the group consisting of a 2,5-dihydroxybenzoate and a 3,5-dihydroxybenzoate that are represented by the following formula (I): where R represents an alkyl group having 4 to 14 carbon atoms; and irradiating the mixed crystal with laser to detect the sample to be analyzed.