We report, the preparation of nanocomposites having polyimide (PI) as matrix and graphene oxide (GO) as filler, analyses of matrixfiller interactions, and enhancements in thermomechanical properties of PI/GO as compared with pristine PI. The matrixfiller interactions were analyzed by H-1 NMR, X-ray photoelectron spectroscopy, and density functional theory calculations. The data suggested stronger matrixfiller interactions in PI/GO as compared with PI/G composites. The stronger matrixfiller interactions and homogeneous dispersion of fillers lead to a significant enhancement in mechanical properties in PI/GO nanocomposites. Thus, with just 1 wt% GO content, the modulus of PI/GO composite increased by similar to 106% as compared with pristine PI. Finally, thermal expansion coefficients of the nanocomposites are also investigated. A plausible hypothesis has been proposed in the text to explain the observed matrixfiller interactions and the subsequent property enhancements in nanocomposites. POLYM. ENG. SCI., 52:2530-2536, 2012. (C) 2012 Society of Plastics Engineers