Peutz-Jeghers syndrome(PJS) is an autosomal dominant disease which is characterized by melanin spots on lips and buccal mucosa, and multiple gastrointestinal hamartomatous polyps. Patients are at risk of forming carcinomas in the gastrointestinal tract, uterus, ovary, breast and other organs. The LKB1(STK11) gene at chromosome 19p13.3 has been identified in 1998 as the causative gene for PJS, and germline mutations of this gene have been detected in about 50 PJS families. These mutations include nonsense mutations, frameshift mutations and missense mutations, all of which are assumed to inactivate the LKB1 gene. LKB1 gene appears to be a tumor suppressor gene, and inactivation of this gene through germline mutation and loss of normal allele may develop hamartomatous polyps. However, the function of LKB1 and mechanism of carcinoma formation are still unclear.