A dead dog was found “cut in half” and left to rot near three other canine carcasses.
Owners have been warned to keep their pets on a tight leash by the RSPCA after the grim discoveries on farmland near Mile Oak, Portslade.
The news comes amid reports of thieves trying to kidnap dogs in city parks.
Elizabeth Dillistone, 19, found the mutilated corpse as she was walking along a path.
She said: “I was just passing by when I saw the dead dog in a field.
“There was only its back legs and half of its body left. It looked like a bull terrier but it had clearly been cut in half and just left there.
“It was horrible - I can't imagine who would do something like that.”
Three more dead dogs were found nearby on the same morning two weekends ago.
One was discovered wrapped in a bedsheet and lying buried in a shallow grave on Mile Oak Farm.
Farmer David Cross, who found the corpse, said it “hadn't been there long”.
He said: “Whoever dug the grave didn't bury it properly. It was a very large dog with pale coloured fur.
“It was in the horse paddock so I just covered it up again.”
Two more dead dogs were found near the farm on the same morning, according to one walker who did not wish to be named.
She said: “They were bull terrier types, just lying in a field. It's so cruel and disgusting.”
A group called Brighton Dogwatch has been set up on Facebook and posters have been distributed warning pet owners to be careful when out walking.
An RSPCA spokeswoman said: “We are extremely concerned about the discovery of these dead dogs and would like to hear from anyone with any information as to what happened to them and who they belonged to. Calls can be made in confidence to the RSPCA on 03001234999.
"Dog walkers should take care when out walking with their pets and keep a close eye on them to ensure they are safe."