The decision was made after a vote by the clubs. Some of whom struggled to find seven subs for the bench last season.
Carling Cup and FA Cup matches will continue to allow seven subs to match the Premier League but all League games and Johnstone's Paint Trophy matches will use just 5.
"This was felt to be a sensible and prudent step given the financial challenges facing many football clubs and the commitment made earlier this summer to adopt Uefa's Financial Fair Play framework," a League spokesman said.