We have studied the fragmentation dynamics of the protonated 2-, 3- and 4-hydroxybenzophenones (2H+, 3H+ and 4H+, 191 m/z) obtained by CID (“Collision Induced Dissociation”) technique coupled to Mass Spectrometer with electrospray source (MS-ESI). The CID-fragmentation patterns involve the C7OH5+ (105 m/z) and C7O2H5+ (121 m/z) cations, for which the intensity ratio is typical to the isomer considered. 2H+ and 3H+ yield preferably C7O2H5+ (121 m/z) and C7OH5+ (105 m/z) respectively, while 4H+ yields both cations in similar quantity. The fragmentation pathways were analyzed and discussed, taking into account the “model of free-proton” and results from computational calculations at B3LYP/6-311++G(d,p) level of theory. CID/MS-ESI fragmentation technique employed to characterize hydroxybenzophenone isomers. Main structures in the spectrum: Parent cation (199 m/z), C7O2H5+ (121 m/z), C7OH5+ (105 m/z).