Luminescence polarization was measured on strained GaAs samples fabricated as a spin polarized photocathode. Photoluminescence (PL) spectrum of the strained GaAs layer showed large polarization at the band edge in comparison with that of the GaAs substrate. The increase of the band gap and the splitting of the valence band were observed in luminescence polarization spectra of photoluminescence excitation (PLE) although they are not clear in the PLE intensity spectra. Spin relaxation time and lifetime of electrons in the strained GaAs layer were measured by using a mode-locked Ti: sapphire laser and a streak camera. The spin relaxation time and the electron lifetime were 105 ps and 45 ps at room temperature, respectively. From the temperature dependence of spin relaxation time, the spin relaxation of our strained GaAs photocathode was found to be mainly caused by electron scattering by holes with simultaneous exchange interaction.