Choose the right litter box
Use a low-sided box your rabbit can easily hop into. Fill it with paper-based or wood-pellet litter (never clumping cat litter).
Put hay in the litter box
Rabbits like to eat and poop at the same time. Place fresh hay in one end of the box to encourage use.
Place the box where your rabbit already goes
Rabbits usually pick a corner. Put the litter box there instead of trying to change their habits.
Limit space at first
Start with a smaller area or pen so the rabbit learns where the bathroom spot is before roaming freely.
Move accidents into the box
If your rabbit poops outside the box, place the droppings inside it so they learn the scent cue.
Be patient and consistent
Most rabbits learn within a few weeks. Clean accidents with vinegar to remove smells.

Tip: Spayed or neutered rabbits are much easier to litter train and more consistent.