Three surface modifiers, namely, aminopolyether (D2000), phenyl isocyanate, and poly(ethylene glycol) (PEG800), which have different affinities to the hard and soft segments in polyurea, were used to synthesize functionalized graphite oxides (GO). The PEG800-modified (PEG800-GO) and phenyl isocyanate-modified (i-GO) GOs were highly exfoliated and dispersed in DMF, whereas the D2000-modified GO (D2000-GO) produced some precipitates. Polyurea/GO composites were prepared using a solution-blending method, in which functionalized GO platelet suspensions in dimethyl formamide were used. Results show that PEG800-GO and i-GO are uniformly dispersed throughout the polymer matrix on a nanoscale, whereas D2000-GO forms visible aggregates. The well-dispersed GO platelets improved the thermal stability and mechanical properties of polyurea. PEG800-GO, which has a strong affinity for the soft segments, shows a more significant reinforcing effect. At 2.0 wt % GO loading, the tensile strength of polyurea was enhanced by ∼75%. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39775.