Around 21, 000 members had until midday to cast their votes and the result will be announced in Stirling tomorrow morning.
A vote was triggered following Jim Murphy's general election defeat in May. MSPs Ken Macintosh and Kezia Dugdale are standing to replace him.
Mr Macintosh, the representative for Eastwood, said: "I recognise that I am the challenger candidate but I want to re-claim our Party on behalf of the members, I want to give you and the people of Scotland hope. I want us to win again."
Meanwhile, Ms Dugdale said: "We have the chance to choose a fresh start for Scottish Labour. If I win this election it will be a clear signal of a new generation ready to take Scottish Labour forward."
Cowdenbeath MSP Alex Rowley, North East representative Richard Baker and Glasgow City Council Leader Gordon Matheson are standing for deputy.
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