Sicily and Sardinia are the two Italian destinations where a ferry crossing is often part of the trip rather than an alternative to it, and pet travel needs to be planned at the booking stage, not the port — pets have to be declared as part of the reservation, whether that's made online, by phone, or through a travel agency.
Provision varies noticeably by operator. Grimaldi Lines and Minoan Lines allow all companion animals covered under EU Regulation 576/2013 on board, with dedicated accommodation areas for dogs and cats; Grimaldi specifically provides kennels for pets over 6kg, while smaller pets travel in their own carrier. Moby offers specially designed pet-friendly cabins where animals can stay with their owner rather than in a kennel, though availability is limited and worth booking early. Across most lines, pets are generally kept out of indoor public areas like lounges and restaurants, but are allowed on open deck areas on a leash and muzzle — and many owners simply keep their pet in the car on the vehicle deck for shorter crossings, which is usually permitted with regular checks allowed.
The same document set applies here as everywhere else: EU pet passport or Health Certificate depending on residency, microchip confirmation, and rabies vaccination proof, all of which can be checked at boarding.