To achieve detection, monitoring, and automation of starch graft copolymerzation at any time, the investigation is being made according to luminescence of free radicals produced in the reaction. The investigations on the fluorescence spectra of starch-water suspension excited by ultraviolet (UV) light and its characteristics contribute to study the characteristics and mechanisms of free radicals coming into being, emitting, and disappearing. Fluorescence spectra of starch, dextrose, sucrose, and maltose excited by 260-nm light are compared and their similarities further verify that this fluorescence comes from the transition from nonbonding, namely n electrons in the hetero-atom (O) of the functional group (C-O-C) called ether linkage, to the antibonding orbital 'sigma'*. The functional group is a part of six-membered ring structure in starch molecule. Meanwhile, the experimental results indicate that relative peak intensity of fluorescence emitted by 1% starch suspension comes to climax when starch suspensions with different concentrations are excited by the same wavelength.