The nitrogen effect on enhancement of oxygen precipitation in Czochralski-grown silicon wafers has been investigated by means of a preferential chemical etching technique and secondary ion mass spectroscopy. The precipitate enhancement is evident in an oxygen out-diffused region in which oxygen precipitation does not normally occur. Incorporation of the nitrogen atoms in substitutional sites to generate very stable microdefects in Czochralski-grown silicon crystals can explain the nitrogen effect on oxygen precipitation.