Surface functionalization effect of graphene oxide (GO) on its liquid crystalline and assembly behavior was investigated to examine the potential of surface modification strategy to produce a strong assembled structure. As a model study, a carboxylated GO (GO-COOH) was synthesized and its liquid crystalline and assembly behavior were systematically compared with pristine GO. Based on this study, we found that the transition concentration of GO from isotropic to biphasic phase decreased with carboxylation and the resulting lamella-assembled structures of GO-COOH exhibited much higher mechanical properties compared to GO after Ca2+ ion cross-linking.