1.1. Objective: Gitelman syndrome (GS) is an autosomal reces sive tubular disorder characterized by metabolic alkalosis, hypo kalemia, hypomagnesemia and hypocalciuria. GS is mostly caused by inactivating mutations of the SLC12A3 gene. The purpose of this study was to describe the clinical features of a GS patient and investigate the underlying mutations of SLC12A3 gene in the ped igree. 1.2. Methods: A patient suffering from muscle weakness was clin ically diagnosed as GS. Clinical data of the proband were studied retrospectively. All of his family members were screened for SL C12A3 gene mutations. 26 exons and exon-intron boundaries of SLC12A3 gene were amplified by Polymerase Chain Reaction(P CR). PCR products were sequenced directly. 1.3. Results: The proband had hyperreninemia but hypoaldoster onemia, which was distinct from the cases previously reported. The proband and his sick brother were found to have the same compound heterozygous mutations (c.917C>T and IVS 14-8T>C) of SLC12A3 gene. Each mutation was detected in paternal and maternal genomic DNA, respectively. The proband’s healthy brother had one mutation (c.917C>T) only. IVS 14-8T>C was a novel splicing site mutation that had never been reported. 1.4. Conclusion: Hypoaldosteronemia was found in a GS patient. A novel heterozygous splicing site mutation of the SLC12A3 gene was reported, expanding the spectrum of SLC12A3 gene muta tions.