PDSA vets said chocolate was one of the biggest threats as it contains theobromine, which is highly poisonous to animals.
There is enough theobromine in an average bar of dark chocolate (700mg per 30g-45g bar) to fatally poison a Yorkshire terrier, according to the charity.
Raisins, sultanas and currents found in mince pies, Christmas pudding and cake could also be highly toxic and should never be fed as treats, the PDSA added.
Last December, the Veterinary Poisons Information Service (VPIS), received 345 calls about pets poisoned with chocolate. They also received around 60 calls about grape, raisin and fruit cake poisoning during the festive season.
Special dog chocolates, designed for pets, are widely available.
The organisation's warning comes as the PDSA launches its Pet Fit Club, which will see five overweight dogs and six cats attempt to stick to a new six-month diet and exercise plan in a bid to lose weight.