Officers were called to reports of an 18-year-old man found with a stab wound in Dominion Road, Worthing, at 5.20pm, Sussex Police confirmed.
The man was taken to Royal Sussex County Hospital in Brighton for treatment.
Police officers arrested two teenage boys on suspicion of causing grievous bodily harm, said police.
Inspector Will Keating-Jones said: “We had a significant police presence in the area and were able to swiftly detain two suspects.
“The incident has been contained and there is no risk to the public.”
Anyone witnesses or anyone with information about the incident should contact police on 101, quoting Operation Quebec.