The structural stabilities of nitrosoketene and its tautomers were investigated using ab initio and DFT method of calculations employing 6-31++G(d, p), cc-pVDZ basis sets. Additionally MP2/6-31++G(d, p) and G3 calculations were performed. Nitrosoketene (I) and structure III were found to be the most stable and the least stable tautomers, respectively. The gas phase deprotonation energies have been determined using Gaussian-2 (G2) method. According to the deprotonation calculations, all the species should be more acidic than water and the acidity order is III > II > I.