Ambulances were called to the site at inner-city Camperdown about 8.30am on Tuesday and found a 22-year-old man with stab wounds.
Police were told the alleged attacker got on a bus at nearby Parramatta Rd not long after the incident.
A short time later, a 14-year-old boy was arrested near Royal Prince Alfred Hospital, which neighbours the university.
The injured man was taken to the same hospital in a stable condition.
NSW Police forensic investigators at the scene of an alleged stabbing at the University of Sydney. (Dan Himbrechts/AAP PHOTOS)
A crime scene has been established at the university campus and the boy is being questioned by police.
The teen did not know the man before the alleged stabbing, police said.
A Sydney University spokeswoman said a police operation was under way on the campus and staff were working with authorities.
"As a precautionary measure there may be an increased security and police presence on campus while investigations continue," she said in a statement.
Police assured the public there was no ongoing risk to the community.
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