Numerous studies have suggested that K C channels regulate a wide range of physiological processes in mammalian cells. However, little is known about the specific function of K C channels in germ cells. In this study, mouse zygotes were cultured in a medium containing K C channel blockers to identify the functional role of K C channels in mouse embryonic development. Voltage-dependent K C channel blockers, such as tetraethylammonium and BaCl 2 , had no effect on embryonic development to the blastocyst stage, whereas K 2P channel blockers, such as quinine, selective serotonin reuptake inhibitors (fluoxetine, paroxetine, and citalopram), gadolinium trichloride, anandamide, ruthenium red, and zinc chloride, significantly decreased blastocyst formation (P!0.05). RT-PCR data showed that members of the K 2P channel family, specifically KCNK2, KCNK10, KCNK4, KCNK3, and KCNK9, were expressed in mouse oocytes and embryos. In addition, their mRNA expression levels, except Kcnk3, were up-regulated by above ninefold in morula-stage embryos compared with 2-cell stage embryos (2-cells). Immunocytochemical data showed that KCNK2, KCNK10, KCNK4, KCNK3, and KCNK9 channel proteins were expressed in the membrane of oocytes, 2-cells, and blastocysts. Each siRNA injection targeted at Kcnk2, Kcnk10, Kcnk4, Kcnk3, and Kcnk9 significantly decreased blastocyst formation by w38% compared with scrambled siRNA injection (P!0.05). The blockade of K 2P channels acidified the intracellular pH and depolarized the membrane potential. These results suggest that K 2P channels could improve mouse embryonic development through the modulation of gating by activators.