Mass Spectrometry has become a powerful tool in proteomics research to precisely determine the molecular mass of peptides and proteins as well the sequences. In tandem mass spectrometry, fragmentation of peptides and proteins gives sequence information for protein identification as well as for the identification and localization of post-translational or other covalent modifications. Mass determination and the Characterization of proteins can be done through Mass Spectrometry. For Ionization of proteins in Mass Spectrometry two methods are used. The methods used are Electrospray Ionization and the matrix-assisted laser desorption/Ionization. Top-down approach and Bottom-up approach are used for the analysis of protein.