Glycogen storage disease type Ia (GSDIa) is an autosomal recessively inherited disease characterized by poor tolerance to fasting, growth retardation, and hepatomegaly resulting from accumulation of glycogen and fat in the liver. Germline mutations of glucose-6-phosphatase (G6PC) gene have been identified as a cause of GSDIa. In this study, we performed mutation analysis in five Chinese GSDIa patients belonging to five unrelated families by direct DNA sequencing. All patients were clinically classified as GSDIa. Mutation analysis of the G6PC gene revealed that all patients carried biallelic G6PC mutations (p.Ile341Asn, p.Ala274Val, p.Phe80Ile, p.Gly118Asp, p.Arg83His, c.262delG, and c.648G>T). Of the seven different mutations identified, three were found to be novel. All of the novel mutations were missense (p.Ala274Val, p.Phe80Ile, and p.Gly118Asp). The c.262delG mutation which leads to a frame-shift and truncated forms of glucose-6-phosphatase was present in three unrelated patients (one homozygote and two heterozygotes).By direct DNA sequencing, three novel G6PC variations were identified which expanded the G6PC mutation spectrum, and provided conclusive genetic evidences for the definitive diagnosis of the Chinese patients.