We measured systematically the influence of relative humidity on the photoluminescence of porous silicon (PS) prepared by electrochemical etching. Measurements were carried out at room temperature in the range of relative humidity (RH) 100-1%. In contrast to dramatic changes of electrical conductivity in PS the variation of photoluminescence (PL) at different RH values was less pronounced. Weak changes of the maximum position, halfwidth and intensity of PL were observed. Typical of all the dependencies on RH were very long time constants amounting to tens of hours.