A simple method to modify thermal-exfoliated graphene nanosheets (T-GNS) by using streaming ozone under different time and temperature is described in this paper. The results indicated that a wide variety of oxygen-containing groups such as C-OH, C-O-C, C=O and COOH could be introduced on the surface of T-GNS by ozone treatment. Especially when ozone modification was taken under 80 degrees C for 20 min, the atomic ratio of O/C was increased to 0.503, and the percentage of carboxyl groups was up to 14.37%, which was more than 10 times compared with the original T-GNS. In addition, it is worth mentioning that ozone treatment under a moderate temperature could cause etching on the edge of T-GNS and form porous structure in basal plane. As a result, the dispersion of ozone-treated T-GNS in aqueous solution was greatly improved, and the enhanced oxygen-containing groups and dispersion would facilitate its further functionalization and application. (C) 2013 Elsevier B.V. All rights reserved.