Abstract We have characterized the mechanical behavior of aligned carbon nanotube (CNT) arrays that serve as foam-like energy absorbing materials, by using atomic force microscope indentation. It is shown that the mechanical properties (e.g. elastic modulus, adhesion force, and energy dissipation) of aligned CNT arrays are dependent on the length of CNTs as well as chemical environment that surrounds CNT arrays. More remarkably, it is found that CNT array made of CNTs with their length of 10μm exhibits the excellent damping property (i.e. energy dissipation) higher than that of a conventional composite such as Kevlar. It is also shown that the energy dissipation of CNT arrays during loading–unloading process can be reduced by the solution surrounding CNT array, and that the decrease of energy dissipation for CNT array due to solution depends on the solution type, which mediates the interaction between individual nanotubes. Our study sheds light on the design principles for CNT array-based foam-like materials.