Potential dependences of the photocurrent and visible photoluminescence (PL from p-type porous silicon (p-PS) in 0.2 M Na2SO4 aqueous solution were investigated. When the potential became more negative than -0.6 V, a cathodic photocurrent was observed and PL was quenched. When the potential was swept back in the positive direction, the PL intensity increased, the photocurrent decreased, and both returned to the initial values. PL spectra measurements showed that the quenching of the PL intensity was accompanied by a blue shift of the peak wavelength as a result of the selective quenching of the red portion of the PL spectra, The experimentally observed results can be explained by considering the dependence of electron accumulation on the conduction band levels in PS layer, which is in turn related to the Si nanocrystalline size.