During the protest, teachers of students of Jaffna University held placards and demanded the immediate release of the four students.
Suresh Premachandran, TNA parliamentarian who represents the Jaffna constituency, said over 1,000 people joined the peaceful protest.
He said this was the first public protest in Jaffna since the LTTE was defeated three years ago.
According to police, the four students were arrested for trying to stage an illegal march.
The Army and police had conducted a search operation in the dormitories of Jaffna university last week looking for LTTE propaganda material after students tried to mark the LTTE "heroes week", the last week of November when the Tamil Tigers used to commemorate fallen cadres.
Jaffna, the cultural capital of the Tamils and its university was the centre of the LTTE activities during its over three-decade-long separatist campaign.
