“I wanted a name on my shirt that represented who I am and I feel I have no connection with the Alli surname,” the England international, 20, told the Tottenham website ahead of his side’s opening game at Everton.
“This is not a decision I have taken without a lot of thought and discussion with family close to me.”
Alli’s mother, Denise, revealed earlier this year that she gave her son away when he was 13 as she was battling alcoholism.
He was raised by another couple, Alan and Sally Hickford.
Alli scored 10 Premier League goals and provided nine assists last season, earning him the Professional Footballers’ Association (PFA) Young Player of the Year award and a place in England’s Euro 2016 squad.