Race was still very fundamental factor in deciding who to vote, although both parties denies this. Obama's win in Mississippi was not a surprise as Clinton's staff conceded to this weeks ago.
"Now we look forward to campaigning in Pennsylvania and around the country," Maggie Williams, Clinton's campaign manager, said in a written statement that congratulated Obama on his victory.
The Illinois senator had 1,585 delegates to 1,473 for Clinton. It takes 2,025 to win the nomination.
Neither of the two rivals appears able to win enough delegates through primaries and caucuses to prevail in their historic race for the nomination, a development that has elevated the importance of nearly 800 elected officials and party leaders who will attend next summer's national convention as unelected superdelegates.
Obama leads Clinton among pledged delegates, 1,374-1,226 in The Associated Press count, while the former first lady has an advantage among superdelegates, 247-211.