"I am not a candidate for the post of NATO secretary general," Sikorski told journalists.
The term of NATO Secretary General Jaap de Hoop Scheffer expires on July 31.
Belgium's Le Soir newspaper earlier reported that Poland's Sikorski, along with Anders Fogh Rasmussen, the Danish prime minister who supported the U.S. invasion of Iraq and addressed NATO operations in Afghanistan in his New Year speech, were top candidates to head the military alliance.
Rasmussen's office said the Danish politician would not seek the post.
Czech Deputy Prime Minister Aleksander Vondra, Norwegian Defense Minister Anne-Grete Strom-Erichsen, former Bulgarian Foreign Minister Solomon Passy and two Canadian politicians, Defense Minister Peter MacKay and former Deputy Prime Minister John Manley are also seen as potential candidates, Poland's Rzeczpospolita newspaper said.