A metal-organic framework, SDMOF-1, with rigid pores of about 3.4 Å, which is appropriate for accommodating C 2 H 2 molecules, exhibits high C 2 H 2 adsorption capacity and great separation capability of the C 2 H 2 /C 2 H 4 mixture. This work provides a new method to design aliphatic MOFs with a molecular sieving effect to realize efficient gas separation.