The incident happened on a route 148 bus in Walworth Road just before 6.30pm yesterday (March 21).
Officers and London Ambulance Service crews attended and found a man who had been stabbed.
He was taken to hospital where his injuries were assessed as non-life threatening.
No arrests have been made as police enquiries continue.
A spokesperson for Metropolitan Police said: “Detectives are appealing for witnesses following a stabbing that occurred on a 148 bus in Walworth.
“On Friday, 21 March police were on patrol and were flagged down by a member of the public at 6.27pm to a 34-year-old man with stab wounds in Walworth Road, SE17.
“London Ambulance Service and London Air Ambulance Service attended.
“The man was taken to hospital. His injuries are neither life-changing nor life-threatening.
“No arrests have been made at this early stage in the investigation.
“Anyone with information is asked to call 101 reference CAD 6596/21March.”
