The IR and Raman spectra of N-C1-phthal imide were recorded for polycrystalline samples. The fundamental frequencies were tentatively assigned on the basis of a C2vmolecular symmetry by comparison with those of phthalic anhydride and phthalimides. The band shifts from the related compounds are discussed in terms of the mechanical coupling among the fundamental vibrations and of the electronic resonance structures. The N-C1 vibrations are compared with those of N-C1-maleimide and N-C1-succinimide.