In the title rhodium(I) complex, [RhCl(C8H12)(C5H12N2S)], N,N′-diethylthiourea acts as a monodenate S-donor ligand. The rhodium(I) coordination sphere is completed by the Cl atom and the COD [= 1,5-cyclooctadiene] ligand interacting through the π-electrons of the double bonds. If the midpoints of these two bonds are taken into account, the Rh atom exhibits a distorted square-planar coordination. The syn conformation of the N,N′-diethylthiourea ligand with respect to the Cl atom is stabilized by an intramolecular N—H⋯Cl hydrogen bond. A weak intermolecular N—H⋯Cl interaction links molecules along the a axis.