The pure rotational spectra of five isotopic species of thiophosphoryl chloride, SPCl3, have been examined in detail in the frequency range 26–110 GHz. This study has shown that the frequencies previously reported for the rotational transitions of three symmetric-top species of SPCl3in the ground state are, in fact, due to molecules in the vibrationally excited statev6= 1. In this work we have measured for the first time rotational transitions for the32SP35Cl3,34SP35Cl3, and32SP37Cl3symmetric-top species in their ground vibrational states. In order to determine an accurate molecular geometry, the spectra of the asymmetric-top species32SP35Cl237Cl and32SP35Cl37Cl2were also recorded. The data obtained have been analyzed to yield values for rotational constants and quartic centrifugal distortion constants. Our results have been used, together with literature vibrational data, to refine an accurate harmonic force field for SPCl3. We have also evaluated effective, substitution, average, and approximate equilibrium values for internuclear parameters. The ground state average structural parameters of SPCl3arerz(PS) = 1.8835(7) Å,rz(PCl) = 2.0093(3) Å, and <(SPCl) = 116.35(2)°.