The incident happened in Cambridge Avenue near Falconwood Parade just before 9.30pm yesterday (July 28).
Officers attended the scene after the boy took himself to a nearby hospital.
Co-op Welling police crime scene: Live incident updates
His injuries were confirmed to be non-life threatening or changing.
A crime scene has been put in place while officers investigate the circumstances.
No arrests have been made as police enquiries continue.
A spokesperson for Metropolitan Police said: “On Monday, 28 July at 21:27hrs police were made aware of a stabbing in Cambridge Avenue, Welling.
“Met officers attended the scene after a 15-year-old boy self-presented at a near-by hospital.
“His injuries were confirmed to be non-life threatening or changing.
“A crime scene has been put in place while officers investigate the circumstances.
“At this early stage, no arrests have been made.
“Enquiries remain on-going.
“If you saw, or have any information about the incident, then please contact police on 101 stating CAD7617/29July.
“You can also speak with independent charity Crimestoppers on 0800 555 111 to remain anonymous.”
