The Scottish SPCA was alerted on Friday after a member of the public made the discovery at the Bathgate Hills and handed them into a vets.
The kittens are now in the care of the charity’s Edinburgh and Lothians Animal Rescue and Rehoming Centre.
Inspector Jenni Surgeon said: “The kittens are around a week old and were found in a bin bag which was full of wet, dirty towels.
“They are far too young to be away from their mum but despite this they are in okay condition.
“We are very concerned for the welfare of their mother.
“There is a chance she has died but if not she will be extremely distressed at having her kittens taken away from her so soon.
“The kittens are now receiving round the clock care from one of our staff members, which involves them being syringe fed throughout the night.
“Once they are old enough we will be looking to find them loving new homes.
“This was an extremely cruel act and if the kittens hadn’t been discovered they would have died.
“We would urge anyone who knows who may have dumped these helpless animals to contact our helpline on 03000 999 999.”
Abandoning an animal is an offence under the Animal Health and Welfare (Scotland) Act 2006 and anyone found guilty of doing so can expect to be banned from keeping animals for a fixed period or life.