The 21-year-old centre-back, who spent a time on loan at Bristol Rovers last season, has moved to Brisbane Road on an initial one month loan deal.
"I'm looking forward to the prospect of a month of senior football," Oji told Orient's official website.
"It was great to be part of a winning team at Bristol last year who went on to get promoted. If I do well, maybe I can stay here for a little longer."