Porous silicon is treated in NH3 gas by rapid thermal annealing. FTIR spectra indicate that the surface of the sample is covered with Si(NH)2 and Si3N4 species. ESR signal shows that the sample has rather low density of dangling bonds. The photoluminescence intensity of the treated sample de-creases slightly compared to the sample without the treatment and is very stable while storing in at-mosphere. These results show that nitride can be an excellent passivation film on porous silicon and may be important to the practical applications.