A narrow size distribution of graphene sheets is critical to there application. Although several strategies have been demonstrated to classify the polydispere graphene oxide (GO), a precursor of graphene sheets, into various specified monodisperse fractions, few reports have revealed the size separation of graphene sheets straightly. Herein, a straightforward and efficient approach for size separation of mechanically exfoliated graphene sheets is proposed. The original graphene sheets (S0) have been separated into two portions with smaller (S1) or larger (S2) lateral dimensions in a weak alkaline buffer via electrophoresis, based on the zeta potential of graphene colloid under different pH values. It was found that the electrophoresis velocities of graphene colloids increase when their diameters decrease. In this way, graphene sheets of different sizes and properties can be separated successfully. Further study on the as-separated components indicated that small-size graphene sheets (S1) display blue shift signals in both ultraviolet-visible and raman spectroscopy, as well as a distinct fluorescent compared with large-size (S2) and original ones (S0). As electrode materials, S2 had a faster charge transfer and higher specific capacitance than that of S1 and S0. The feasible and effective method provided in this work to classify mechanically exfoliated graphene sheets are potentially beneficial to the broad applications of graphene. (c) 2017 Elsevier Ltd. All rights reserved.