The heterogeneity of the surface energy of multiwalled carbon nanotubes (MWNTs) before and after the adsorption of poly(acrylic acid) (PAA) at 77 K was investigated by a nitrogen probe adsorption technique in a wide range of pressures. The adsorption energy distributions (AEDs) were calculated from the low-pressure data of isotherms (i.e., the data of submonolayer adsorption) using the regularization method. Based on the AED, two types of dominant energetic surfaces are identified and assigned to the graphite-like carbon and disordered carbon or defects in the pure MWNTs, respectively. While the adsorption amount of PAA is raised, a significant decrease in the contribution of higher-energy surface in AEDs is observed for those PAA-adsorbed MWNTs. It is thus demonstrated that PAA prefers interacting with higher-energy surfaces to lower-energy surfaces in MWNTs. Nitrogen probe adsorption measurements including low-pressure data are shown to be a feasible and effective tool to characterize the heterogeneity of structure and surface properties of porous materials. (C) 2004 Elsevier Inc. All rights reserved.