Two members of the pro-opposition newspaper Uthayan were badly injured and property was damaged, the BBC reported.
Six staff members and a driver who distributed the publication were in the office at the time of the attack, said E Saravanapavan, the owner.
He said the attackers waved cricket stumps and shouted in Sinhala, the country's majority language.
The attack was the fourth this year on Tamil-language newspapers or their distributors. The Uthayan's office has repeatedly attacked over the years. Several of its staff members have been killed.
The newspaper's owner is also a parliamentarian in the Tamil National Alliance opposition party.