In the beginning of 21^(st) century, developing an analytical technique to efficiently identify polar biornolecules is essential for the research in the post genomic era. A dramatic progress in the development of soft ionization methods, i.e. matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI), for the analysis of biornolecules with high polarities in the mass spectrometry has been achieved in the past twenty years. Thus, MALDI and ESI play very important roles in the current age. This article will be centered on the history, characteristics, ionization mechanisms, and instrumentation of MALDI.