The incident happened in Pawsons Road at 7.45pm last night (May 23).
Officers, London Ambulance Service, and an air ambulance attended and found a man injured.
He was taken to hospital for further treatment.
Despite the efforts of emergency services, he was pronounced dead a short time later.
His next of kin have been informed.
A post-mortem examination will be scheduled in due course.
It is believed that the man sustained his injuries after an altercation nearby in Mayo Road.
A crime scene remains in place following the incident.
No arrests have been made as police enquiries into the circumstances continue.
A spokesperson for Metropolitan Police said: “A murder investigation is underway following a stabbing in Croydon.
“Police were called at approximately 7.45pm on Tuesday, 23 May to reports of a man, aged in his 20s, suffering stab injuries in Pawsons Road, Croydon.
“Officers, London Ambulance Service and London’s Air Ambulance all attended and the man was taken to hospital – despite the efforts of the emergency services, he was pronounced dead a short time later.
“His next of kin have been informed.
“A post-mortem examination will be scheduled in due course.
“At this early stage it is believed the man sustained his injuries following an altercation in nearby Mayo Road.
“A crime scene remains in place.
“No arrests; enquiries into the circumstances continue.
“Anyone with information that could assist police is asked to call 101 or tweet @MetCC and quote CAD 6826/23May.
“Alternatively contact the independent charity Crimestoppers anonymously on 0800 555 111.”
