Police say it happened at the station for the B and Q trains in Flatbush.
Investigators believe there was a dispute before the stabbing.
Authorities say the victim was taken to Kings County Hospital in stable condition.
Subway riders say police have to do more to protect commuters.
"I think we got to do better, especially with our security. Where are the thorough pat-downs, where is everybody? Everybody's here after the commotion," one rider said.
Police have not said what the dispute may have been about. The suspect fled the station.
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