Hypokalemic periodic paralysis (HypoPP) is an autosomal dominant disorder characterized by periodic attacks of muscle weakness associated with a decrease in the serum potassium level. Several mutations in the skeletal muscle calcium channel α-subunit gene CACNA1S have been documented to be causative for HypoPP, but mutations in other genes have also been implicated in HypoPP. To further reveal the genetic causes of HypoPP, we genotyped members of a five-generational Chinese family with HypoPP patients and identified a novel His916Gln mutation in all male HypoPP patients of the family. Clinical analysis demonstrated that the penetrance of the mutation was complete in male carriers, but we did not find evident clinical features in female carriers. This study expanded the spectrum of CACNA1S mutations associated with HypoPP and demonstrated a gender difference in the penetrance of the disease.