Falling Slowly from Once won Best Original Song this year
Oscars organisers are to limit the number of nominations in the original song category to two per film to make it more competitive.
Enchanted took three of the five nominations for this year's award, as did Dreamgirls in 2007.
However, neither film actually won the prize at Hollywood's biggest awards ceremony of the year.
The changes take effect for 2009's ceremony, along with alterations to the
foreign language film award.
Three of the nine finalists for the foreign language film nomination will now be chosen by a committee.
In the past, all nine films were chosen by a vote of all academy members who had seen a minimum number of eligible films.