At present, the construction of a bimetallic and oriented MOF nanosheet membrane that integrates the advantages of both bimetallic MOF and oriented membranes is highly desirable but also challenging. Herein, we report a vapor phase transformation (VPT) strategy for directly growing a highly oriented bimetallic (Zn/Co) 2 (bIm) 4 (bIm = benzimidazole) nanosheet membrane, based on the conversion of hydroxy double salts (HDS) under bIm ligand vapor treatment. The fabricated strategy includes first the growth of a layer of bimetallic Zn/Co-HDS on a porous tube and then the conversion of the HDS layer into a highly oriented bimetallic nanosheet membrane via the VPT strategy. The formation mechanism of the membrane is discussed. The resulting ultrathin nanosheet membrane with the thickness of about 80 nm exhibits excellent gas separation performance with H 2 permeance of 1.68 × 10 -7 mol m -2 s -1 ·Pa -1 and H 2 /CO 2 ideal separation selectivity of 54.1. This approach shows great potential in large-scale fabrication of nanosheet membranes, especially the bimetallic MOF nanosheet membranes. • A VPT strategy is developed for growing bimetallic MOF nanosheet membrane based on the conversion of HDS. • The achieved bimetallic MOF nanosheet membrane combines the advantages of nanosheets and bimetallic MOFs. • Both HDS layer and VPT strategy cooperatively facilitate the generation of bimetallic MOF nanosheet membrane. • The membrane exhibited excellent molecular sieving performance for H 2 /CO 2 .