Three dogs have been poisoned and one has subsequently by rat bait in Ashenground Woods next to Bolnore Village.
The RSPCA is appealing for information about the incident.
An RSPCA statement says: “It is illegal to put out rat poison where any animal other than rats can be harmed by it and anyone found responsible for putting out the poison that has caused suffering to these dogs could face up to six months in prison and a fine of up to £20,000 under the Animal Welfare Act.
“It is possible that rats poisoned by the bait have been found by the dogs, who then suffered secondary poisoning.”
RSPCA Sussex Chief Inspector Patrick Hamby: “It is a fact of life if you live close to woods as Bolnore Village is that there will be rats nearby.
“The best way to avoid encouraging them into your garden is to remove any food that they may be attracted by - rubbish or pet food for instance.”
Anyone with any information on who is putting out poison near the woods is asked to contact the RSPCA in confidence on 03001234999.