The attack took place on an S-Bahn route between Ostbahnhof and Alexanderplatz, according to local media. The four men beat and kicked their victim before he was able to get out of the train at Alexanderplatz station where a 28-year-old was able to intervene and prevent the attack from going further.
The four men fled the scene and have not been identified.
The man suffered a broken cheekbone and was taken to hospital. The motive of the attack is still not clear.
N-tv reports that this is just one in a series of violent attacks on the Berlin transport system.
On Monday evening the police had to intervene after a man threatened passengers on a train to Potsdam with an axe. According to witnesses, without provocation the man started verbally abusing passengers before swinging the axe around.
Police said the man was seriously intoxicated with alcohol at the time. No one was hurt during the incident.