The widely use of CNTs (single walled carbon nanotube and multi walled carbon nanotube) allows for potential exposure to this new nanomaterial. Most of the previous research on toxicology of CNTs have revealed that CNTs could induce genotoxicity via reactive oxygen species (ROS) indction. However the possible pathway of signal transduction was not completely understood. The aim of this work was to establish a possible role of p21 and hus1 gene in the impaired signaling pathway. Comparison of micronucleus fractions between wild type and p21-/-, hus1+/+ mouse embryo fibroblast (MEF) cells were performed in the experiment. The lower yield of micronucleus ratio in p21 knockout MEF cells indicated that p21 may contribute as an anti-apoptotic factor in the DNA damage signal transduction.