Carbonyl diisothiocyanate (1) and oxalyl diisothiocyanate (2) were synthesized by reactions of phosgene and oxalyl chloride with ammonium thiocyanate, respectively. Their structures were elucidated by single-crystal X-ray diffraction. 1 exhibits weak intermolecular S−O contacts forming a loosely connected network of molecules, whereas 2 exhibits weak intermolecular C carbonyl −O contacts resulting in the formation of layers. Both compounds were further characterized by nuclear magnetic resonance, infrared, and Raman spectroscopy. Quantum-chemical calculations reproduced the experimental structures and enabled the interpretation of the vibrational spectra.