By the use of a home-built research-grade laser time-of-flight mass spectrometer and with a new recently developed new method, matrix-assisted laser desorption ionization (MALDI), the molecular weight of proteins, such as lysozyme, cytochrome C, myoglobin, trypsin, protease and albumin as well as mixtures of proteins are determined. The results demonstrated that with the new method molecular weight of proteins can be determined fastly (witin ten minutes), accurately (absolute error=±0.1%) and sensitively (10^-^1^2～10^-^1^5mol), that is far superior than those traditional methods.

Key words: MOLECULAR WEIGHT, PROTEASE, CYTOCHROME, TRYPSIN, ALBUMINE, PROTEIN, LYSOZYME, MYOGLOBIN, TIME-OFF FLIGHT MASS SPECTROMETRY