The influences of the deep-level concentration of p-type Si substrates on the optical properties of nano-porous silicon (PS) are investigated by deep level transient spectroscopy (DLTS) and photoluminescence (PL). Utilizing a Si substrate with Fe contaminations significantly enhanced the PL intensity of PS. All the PS samples formed on Fe-contaminated silicon substrates had stronger PL yield than that of reference PS without any intentional Fe contamination but the emission peak is not significantly changed. For the PS 1000 sample with Fe contamination of 1,000 ppb, the maximum PL intensity showed about ten times stronger PL than that of the reference PS sample. From PL and DLTS results, the PL efficiency strongly depends on the Fe-related trap concentration in Si substrates.