The official Fenerbahce website carried a photograph of Lille forward Sow arriving in Istanbul on Thursday night, having flown in from Equatorial Guinea where his national team are competing in the African Nations Cup.
It was reported on fenerbahce.org that the 26-year-old would undergo a medical on Friday.
Sow told the Fener official website: "There were of course a lot of teams interested but this was the club I really wanted to join.
"I'm very happy. As soon as I arrived I was very happy to see the excitement here. I'm looking forward to playing in front of Fenerbahce fans."
Reports in Africa suggest Sow has agreed a contract worth 3.2million euros (almost £2.7million) a year with Fenerbahce.
Sow finished as the top goalscorer in Ligue 1 last season, firing 25 goals as Lille won the title.
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