Sec translocon, a protein-conducting channel that is conserved in all organisms, functions in cooperation with several proteins including SecA ATPase, a motor protein for protein translocation. To discuss the mechanism of the protein translocation, detail structural information was needed. The first structural report of Sec protein at high resolution is the crystal structure of SecA ATPase in 2001. In this review, I outline the structural biology of the Sec translocon, especially based on our structural studies over the past 10 years.