The incident happened in Birkbeck Avenue, Greenford at around 8pm on December 4.
Officers initially attended reports of a fight, but discovered two boys aged 16 and 17 suffering stab wounds.
The London Ambulance Service treated them at the scene before taking them to hospital in non-life threatening or changing conditions.
The 16-year-old victim was later arrested on suspicion of attempted murder, affray, and assault occasioning grievous bodily harm.
A 20-year-old man was arrested on suspicion of the same offences.
READ MORE: Dad killed in Willesden crash ‘brightened the lives of all’ and loved Liverpool FC
Both males remain in custody.
Anybody who witnessed this incident or has information that could help police should call 101, referencing CAD 6592/04DEC.
To remain anonymous, contact Crimestoppers on 0800 555 111.
