The three brothers, aged 25, 26, and 35, all received hospital treatment after being stabbed in what GMP described as an "unprovoked attack".
They were attacked in Levenshulme, south-east Manchester, while on a night out on Sunday.
Police said a gang of four or five men stabbed the trio on Chapel Street at about 22:00 BST, with the offenders fleeing the scene immediately afterwards.
The elder of the three brothers was taken to Stepping Hill hospital with serious stab wounds to his lower back, while the other two men were treated at Manchester Royal Infirmary for stab wounds to their backs.
None of the injuries are thought to be life threatening.
"The three brothers were enjoying a night out when they were stabbed in what appears to be an unprovoked attack," said GMP Detective Constable Pete Rickards.
"They had just left the Fiddlers Green on Stockport Road and had cut through Bankley Street onto Chapel Street to head for the Horseshoe pub when they were attacked.
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