The 25-year-old joined the Addicks from Swindon Town in June 2016 and scored seven goals in 28 appearances.
Ex-Manchester United trainee Ajose has had two previous loan spells with his hometown club, in 2010-11 and 2013.
"I sat down with him and he said this was something he wanted, so I told him I wasn't going to stand in his way," Charlton boss Karl Robinson said.
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Bury have signed striker Nicky Ajose on a season-long loan deal from fellow League One club Charlton Athletic.