High degree of preservation of spin states mediated by optical phonons is demonstrated with a positive trion state in a single quantum dot. At the optical phonon resonance suppression of spin relaxation is clearly identified as a dip structures in photoluminescence excitation spectra under cross-circularly polarize detection with respect to a pumping. As a result, distinguishably high degree of circular polarization up to similar to 0.85 is achieved in the absence of external magnetic field, which is no the case for neutral excitons with finite fine structure splitting. The absence of continuum states plays a crucial role for this observation. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim