The ³⁵Cl NQR Zeeman spectrum in a single crystal of perchloro-3-cyclopentenone has been studied for the three lines, v₁=36969.3, v₂=37992.2, and v₃=38365.0 KHz, at 294 K by a pulsed FT NQR spectrometer equipped for automatic measurements. The results of the analyses revealed that the molecule has a C_2-symmetry in its crystal and that the five-membered ring is almost planar. The asymmetry parameters for v₁, v₂, and v₃ are determined to be 0.144, 0.027, and 0.035, respectively. The frequency Split for v₂ and v₃ was explained by the difference in the hyperconjugation between the C=O and the C-Cl o-bonds for the geminal chlorines. The molecular structure was derived from the results.