The incident happened on the 8.54pm service between Edinburgh Waverley and Helensburgh Central on Saturday.
Two people sustained facial injuries. They needed treatment in hospital for a broken nose and minor cuts.
The scuffle allegedly broke out after five to six men all in their 20s got into a disagreement with a family also travelling on board.
The men left the train at Livingston North Station after the fight.
Police are making enquiries into the attack.
Anyone with information is asked to contact 0800 405 040.
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