The structure of fullerenols was directly characterized by combining detection of positive and negative ion mode of laser desorption ionization time-of-flight mass spectrometry.Compared to that of the fullerene,the carbon cage of fullerenol was found to more easily show regular fragmentation peaks in the positive ion mode.However,in the negative ion mode,both fullerene and fullerenol retain the characteristic peaks of carbon cage.This method can be used for the identification and selection of the alkali reaction condition for the synthesis of fullerenols,and the optimal reaction alkali concentration of 1.0 g/mL was obtained.At the same time,this method was also approved that fullereols could be stable in the solvent of DMSO.