Single-ion selectivity with high precision has long been pursued for fundamental bioinspired engineering and applications such as in ion separation and energy conversion. However, it remains a challenge to develop artificial ion channels to achieve single-ion selectivity comparable to their biological analogs, especially for high Na + /K + selectivity. Here, we report an artificial sodium channel by subnanoconfinement of 4′-aminobenzo-15-crown-5 ethers (15C5s) into ~6-Å-sized metal-organic framework subnanochannel (MOFSNC). The resulting 15C5-MOFSNC shows an unprecedented Na + /K + selectivity of tens to 10 2 and Na + /Li + selectivity of 10 3 under multicomponent permeation conditions, comparable to biological sodium channels. A co–ion-responsive single-file transport mechanism in 15C-MOFSNC is proposed for the preferential transport of Na + over K + due to the synergetic effects of size exclusion, charge selectivity, local hydrophobicity, and preferential binding with functional groups. This study provides an alternative strategy for developing potential single-ion selective channels and membranes for many applications.