Abstract: The researches on functions of X ray repair cross complementing(XRCC) genes had promoted the understanding of DNA damage repair processes and the mechanism of cancer induced by genetic instability. The functions of XRCC genes could be identified by studying their mutant phenotypes. Most members of the XRCC genes family participated in several DNA repair pathways, including base excision repair, homologous recombination repair and non-homologous end joining. The identification of XRCC genes and their functions took important parts in DNA damage repairs and genetic stability processes.