On the evening of Napoli's 90th birthday celebrations at their San Paolo stadium on Monday, Milik, 22, walked out on to the pitch wearing a Napoli shirt, reports Xinhua.
Club owner and president Aurelio De Laurentiis posted a message on his Twitter account which said: "Welcome Milik."
"It's an honour to be part of Napoli," Milik wrote on his Facebook page.
"There are fantastic fans with a lot of passion, a great club with a glorious history. I want to make those fans happy."
Milik scored 21 goals for Amsterdam-based Ajax in the past season. He also played alongside Bayern Munich superstar Robert Lewandoski in Poland attack at the European championship.
This website uses cookies.