The Illinois senator will cancel events in midwestern Iowa and Wisconsin and head to his native Hawaii for a one-day trip on Thursday, before throwing himself back into full bore campaigning Saturday, advisor Robert Gibbs said.
Obama's grandmother Madelyn Dunham played an instrumental role in his upbringing and he lauded her as an anchor of his life in his convention speech in August.
"In the last few weeks her health has deteriorated to the point where her situation is very serious," Gibbs told reporters on Obama's plane in Florida, declining to give further details of Dunham's condition.
"It is for that reason Senator Obama has decided to change his schedule on Thursday and Friday so that he can see her and spend some time with her.
He will be returning to the campaign trail on Saturday," said Gibbs, describing Dunham as "one of the most important people in his (Obama's) life.
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Obama has a healthy lead in polls in Iowa and Wisconsin, so cancelling stops in the two states would n