It also overturned suspended one-year sentences handed to three other officers over the August deaths of the prisoners, who were alleged supporters of ousted Islamist president Mohamed Morsi.
The 37, who were being transported from a police station to a prison near Cairo, died after the tear gas was thrown into their closed police van.
The officer given 10 years was the deputy head of the police station who oversaw the transfer.
The four were sentenced for manslaughter after the prosecution's investigation revealed they acted recklessly.
Human rights lawyer Amr Imam told AFP the decision "means that the case is back to square one."
Since Morsi was ousted by the army in July, the military- installed authorities have launched a crackdown on his supporters that has left more than 1,400 killed in street clashes and jailed at least 15,000.
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