The new compound SmMnBi2 has been synthesized by the self-flux method and shown to crystallize in space group I4/mmm with a = 4.5054 (4) Å, c = 20.5914 (19) Å and Z = 4. Its structure comprises two-dimensional square Mn-nets layers, puckered rock-salt-like SmBi slabs and two-dimensional square Bi-nets layers, alternating along the c axis in an …Mn-net–SmBi slab–Bi-net–SmBi slab–Mn-net… sequence. Surprisingly, the atomic arrangement differs from its neighboring compound EuMnBi2 which has similar layers but with a different stacking arrangement. This gives rise to edge-shared square planar MnBi4 polyhedral layers in SmMnBi2 while EuMnBi2 has edge-shared MnBi4 tetrahedral layers. The MMnX 2 (M = alkaline earth/rare earth metals, X = Sb/Bi) family has emerged as topological Dirac or Weyl semimetal candidates, all of them sharing similar structural features. Although SmMnBi2 has a different stacking arrangement to EuMnBi2, its layer structure still makes it a topological Dirac or Weyl semimetal candidate.