Stagecoach staff are examining CCTV to track down the culprit who defecated on seats of the Number 8 bus on Sunday.
The double decker, which was on route to Canterbury, had to undergo a deep clean at the Stagecoach depot following the disgusting find.
A passenger travelling from Thanet said they caught the bus and noticed the smell after going on the top deck.
They added: “Driver informed but said there is nothing they can do until they get back to the depot.”
A photo of the stomach-turning find was also posted to social media, prompting a flurry of disgusted responses including one person who said: “I can smell that picture.”
A spokesman for Stagecoach said information will be passed to police.
They said: “We took the bus out of service as quickly as possible to undergo a thorough clean and disinfection.”
“This was a particularly unpleasant act and we are examining CCTV footage to identify who did this. We will be passing any information we find to the police.”