Compared with layered materials such as graphite and transitional metal dichalcogenides with highly anisotropic in-plane covalent bonds, freestanding metallic two-dimensional (2D) films with atomic thickness are intrinsically more difficult to achieve. The omnidirectional nature of typical metallic bonds prevents the formation of highly anisotropic atomically thin metallic layers. Herein, we report a ligand regulation strategy to stabilize monoatomic platinum layers by forming a unique lamellar superlattice structure with self-assembled organic ligand layers. We show that the interlayer spacings and coordination environments could be systematically tuned by varying programmable molecular ligands with the designed length and structural motifs, which further modulate the electronic states and catalytic performances. The strategy can be extended for preparing lamellar superlattices with monoatomic metallic layers from silver and gold. Such general and delicate synthetic control provides an exciting model system for systematic investigation of the intriguing structure-property correlation of monoatomic layers and promises a molecular design pathway for heterogeneous catalysts.