The Paw Report, the largest pet health study of its kind, surveyed 923 dog owners across the UK about their pet's health and well-being.
Chocolate which is meant for humans contains theobromine, which is toxic to many animals and can prove fatal if eaten, veterinary charity PDSA said.
The study found that owners in the North East are the biggest culprits, with more than a fifth owning up to feeding their dogs the poisonous treat, while owners in the South West are best behaved, with only 1% admitting to giving their pets chocolate.
High-quality dark chocolate poses the biggest risk to dogs, with a small bar containing more than enough theobromine to fatally poison a small dog such as a Yorkshire terrier, the charity said.
PDSA vets and nurses see more than 400 cases of chocolate poisoning in dogs every year and often see a surge in cases around Easter and Christmas.
The charity has also warned people not to give their pets hot cross buns, which contain raisins that are also toxic to animals.
PDSA senior vet Elaine Pendlebury said: "The effects of chocolate poisoning in dogs usually appear within four hours of eating, and can last as long as 24 hours.
"Initial signs can include excessive thirst, vomiting, a sore stomach and restlessness.
"These symptoms can then progress to tremors, an abnormal heart rhythm, raised body temperature and rapid breathing.
"In severe cases dogs can experience fits, kidney failure and can even die."
For Easter pet advice visit www.pdsa.org.uk/Easter.