He told the BBC that he was giving a "very clear indication" about who he was likely to appoint to the post.
But he stopped short of officially confirming it would be Mr Balls before the election results were in, because he thought it was "presumptuous".
He added: "I think you can take it from my answer what I'm planning to do."
In an interview with BBC Newsnight presenter Evan Davis, he added: "I've always said that I don't do measuring the curtains because my focus is on up to 7 May.
"I'm not going to start appointing members of my cabinet, but I think Ed Balls has shown over the last four years, and in this campaign, that he is somebody who is not just capable of being chancellor, but would be an excellent chancellor.
"I'm giving you a very clear indication."
The Labour leader was also pressed on the subject of how much his party would be borrowing at the end of the next Parliament, but did not give a specific answer.
He said Labour would have a surplus on the current budget "as soon as possible" in the next Parliament, and have net debt falling.
But Mr Miliband said he would not pick an "arbitrary number" for borrowing in six years' time.
He was also asked if Labour's borrowing would be bigger at the end of the next Parliament than the Conservative's plan.
"I don't believe it will", he said based on the Tories' failure to meet their borrowing target in this Parliament.
Asked whether the SNP would effectively be calling the shots over any future Labour government, he said: "It ain't going to happen... the House of Commons works in a very simple way. It's for people in the Commons to decide how they vote on measures put before the House of Commons... The SNP aren't going to tell us".
In the first of the series of leaders' interviews with Evan Davis, Lib Dem leader Nick Clegg said he would reject another coalition with the Conservatives if they insisted on their proposed Â£12bn welfare cuts.
And last week David Cameron told the presenter that accusations about the Conservatives being "the party of the rich" made him "more angry than almost anything else".
The full interview can be seen from 19:30 BST on BBC One and online on the BBC's election live page.
Labour leader Ed Miliband has said that Ed Balls "would make an excellent chancellor" should his party win power.