Greater Manchester Police said the suspect had been arrested on suspicion of murder after the other 15-year-old boy died following reports of a disturbance “involving a number of people” in the Moss Side area.
He is in custody for questioning.
The force said the victim was found with stab wounds on Monton Street just after 4.30pm on Monday.
Section 60 powers, allowing officers to stop and search people, are in place in the area until just after 5pm on Tuesday.
Police said enquiries are continuing and additional officers will be in the area over the next few days.
Chief Superintendent David Meeney from the City of Manchester district earlier said: “Our thoughts are with the victim’s family and friends after this tragic and upsetting incident, and our specially trained officers will be supporting them at this difficult time.”
