The p53 signaling pathway plays critical roles in determining the radio-sensitivity of normal tissues but is frequently inactivated in cancer. In various cancer cells, p53 has different effects on radio-sensitivity through complex mechanisms. Acetylation of p53 is an important means of post-translational modifications and is indispensable for its activation that is a reversible enzymatic process. Both acetylation and deacetylation of p53 are involved in the fine regulation of cellular responses to DNA damage and genotoxic stress, such as radiation. Targeting the acetylation of p53 may enable the modulation of radio-sensitivity of cancer cells.