The Carbon Nanotubes have been reported to show hysteresis curves by Nano-indentation tests. To clarify the mechanism of this hysteresis, we conducted Nano-indentation tests to CNT films by using two diamond tips with different curvature radii. The AFM Nano-indentation was to perform penetration of diamond tip into CNT film, which means generation of friction force between diamond tip aspect and CNT tubes aspect. On the other hand, in the case of using spherical diamond tip by which cyclic Nano-indentation tests were conducted, the load-displacement curves became similar to those of carbonaceous coatings. This means that cyclic indentation for CNT made it like continues material. However, after several cyclic Nano-indentation tests to same position, the CNT specimen still showed hysteresis curve. These results indicated that hysteresis of CNT by Nano-indentation was related to friction between CNT tubes each other. © 2013 The Japan Society of Mechanical Engineers.