Dusty star-forming galaxies (DSFGs) have been discovered at z~6–7 in current studies, which offer us unique opportunity to study metal/dust enrichment in the very early Universe and formation of the first generation of massive ellipticals. However, DSFGs confirmed at z>5 are still very rare, discovering more unlensed DSFGs out to higher redshifts is challenging for current facilities. In this talk I will present a brief overview on selection and redshift confirmation of the most distant DSFGs, and discuss related science.