Objective To determine mutations of two common potassium channel subunit genes KCNQ1 KCNH2 causing long QT syndrome (LOTS) in the Chinese. Methods Thirty-one Chinese LOTS pedigrees were characterized for mutations in the two LOTS genes, KCNQ1 and KCNH2, by sequencing. Results Two novel KCNQ1 mutations, S277L in the S5 domain and G306V in the channel pore, and two novel KCNH2 mutations, L413P in the transmembrane domain S1 and L559H in the transmembrane domain S5 were identified. The triggering factors for cardiac events developed in these mutation carriers included physical exercise and excitation. Mutation L413P in KCNH2 was associated with the notched T wave on ECGs. Mutation L559H in KCNH2 was associated with the typical bifid T wave on ECGs. Mutation S277L in KCNQ1 was associated with a high-amplitude T wave and G306V was associated with a low-amplitude T wave. Two likely polymorphisms, IVS11 + 18C > T in KCNQ1 and L520V in KCNH2 were also identified in two LOTS patients. Conclusions The mutation rates for both KCNQ1 (6. 4%) and KCNH2 (6. 4%) are lower in the Chinese population than those from North America or Europe.