Raman spectra of phenothiazine and its radical cation were obtained. Hartree-Fock (HF) and density functional theory (DFT) ab initio calculations were performed to find optimized structures and computed vibrational frequencies. The ab initio structures are compared to previously reported X-ray diffraction experimental results, and the vibrational frequencies are compared to Raman spectra given here as well as previously reported Raman spectra. We have made vibrational assignments for the observed Raman bands, based on the computed potential energy distribution (PED) and isotopic shifts. Our results indicate that the neutral phenothiazine molecule has a nonplanar structure with similar to 153 degrees dihedral angle and the radical cation has a planar (or near planar) structure with similar to 180 degrees dihedral angle.