Animal welfare officers are “extremely concerned” over the suspected poisoning case.
The Scottish SPCA was alerted to the potential poisoning after the cats were discovered in Eyemouth on 17 and 18 May.
The animals belonged to different owners on Queens Road in the town. They were both found near their homes.
Both cats had dried yellow foam around their mouths. The deaths are being treated as suspicious.
SSPCA inspector Stephanie McCrossan said: “These cats were discovered with no visible injuries, just foaming at the mouth, so we’re extremely concerned.
“We are now in the process of having a post-mortem examination carried out to confirm the cause of death.
“Pet owners in the area should be vigilant when letting their cats out of the house and should supervise their animals where possible.
“The poisoning of domestic animals is a huge issue and we deal with a large number of complaints regarding poisonings.
“Poisoning an animal will cause a considerable amount of suffering and, in the majority of cases, a slow and painful death.
“Without any other evidence we cannot say whether these poisonings were deliberate or accidental, so we are appealing to local residents to contact us if they have any information in relation to these concerning incidents.”