The incident happened in Sutherland Avenue near Harrow Road at around 6pm yesterday (November 4).
Officers and London Ambulance Service crews attended and found a boy with injuries to his head.
He was taken to hospital where his injuries were assessed as neither life-threatening nor life-changing.
No arrests have been made as police enquiries continue.
A spokesperson for Metropolitan Police said: “Around 18:00hrs on Monday, 4 November, officers attended Sutherland Avenue, Kensal Green, with the London Ambulance Service following reports of a stabbing.
“A 15-year-old boy was found at the scene with head injuries. He was taken to hospital, where his injuries were assessed as neither life-threatening nor life-changing.
“No arrests have been made, and officers are making enquiries.
“Anybody who witnessed the incident is urged to call 101, quoting crime reference 6091/03OCT.”
