Yes, you can. The rules in the Player’s Handbook and SRD state that:
Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll.Player’s Handbook
While it says sneak attack can only be used once per turn, people sometimes misunderstand that a turn is the period in which a single character gets to perform their actions whereas a round is the period in which everyone gets a turn.
As an opportunity attack occurs on a new turn (someone else’s turn), you can perform a sneak attack both on your turn, and on your enemy’s turn. That is, as long as they provoke an opportunity attack and the other requirements for sneak attack are still being met.
Technically, this means you could also use sneak attack in other rare moments when you get an attack on someone else’s turn.
This is ruling clarified in Wizard’s official sage advice compendium.
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