The striker will spend the 2015-16 campaign at the Amsterdam Arena having played the second half of last term at Crystal Palace.
Sanogo has one goal in 20 Arsenal appearances since joining from Auxerre in 2013, but Arsene Wenger is confident a spell under Frank de Boer will be beneficial to the Frenchman's development.
"He needs to play. He came to us injured and it took us a while to get him to the top level," Wenger told Arsenal's official website.
"He's ready to play now and I'm sure he can be a good signing for Ajax.
"He has an opportunity to play in the Champions League with Ajax, which is good experience. We have a good relationship with them and hopefully he can have a great season."
