Cationic corn starch derivatives containing quaternary ammonium groups with a high degree of substitution were synthesized by reacting corn starch with glycidyltrimethylammonium chloride (GTAC) in a homogeneous manner using 1-butyl-3-methylimidazolium chloride (BMIMCl) as a reaction medium. The influence of reaction time, reaction temperature, the amount of catalyst NaOH and molar ratio of GTAC/anhydroglucose units in starch on the degree of substitution (DS) of products was investigated. The maximum DS value obtained in the optimum reaction condition was up to 0.99. Furthermore, the structure of cationic starch derivatives was characterized by means of Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermal analysis and 1H NMR spectroscopy. The results showed that the ordered crystalline structure of native starch was largely destroyed during the dissolution and functionalization of starch in the ionic liquid BMIMCl, leading to an uniform etherification reaction to be carried out under the homogeneous reaction conditions.