Abstract: Mass spectrometry has become an important analytical tool in biological and biochemical research. Its speed, accuracy and sensitivity are unmatched by conventional analytical techniques. The matrix assisted laser desorption ionization-time of flight MS(MALDI-TOF-MS) and electrospray ionization MS can efficiently solve many questions in proteomics. This review concerns principles and methods of MALDI-MS and ESI-MS. The some applications of mass spectrometry in protein and peptides analysis are shown also.