We studied the defect properties present in rapid thermal oxidized porous silicon (RTOPS) by Electron Spin Resonance (ESR). Two different types of defects are distinguished, one similar to the ones observed in damaged c-Si, and in a-Si. The second one is probably related to the Pbo center at the Si/SiO2 interface. The minimum density of 1016 cm-3 is observed for the as etched and for the 900°C oxidized samples, but reaches a maximum of 8×1018 cm-3for the 600°C samples. The PL intensity anticorrelates with the defect densities, which shows that nonradiative recombination via defects is a very powerful channel in quenching the PL efficiency.