Police said the forest personnel on a routine patrol found an abandoned gunny bag containing the narcotic in Yaanaiparai Theevu near Keelakarai, about 60 km from here in the Gulf of Mannar.
They said the ganja might have been brought there for being smuggled to Sri Lanka. Further investigation was on.
This is the second haul of ganja in this region in the last few weeks.
About 250 kg of ganja worth about Rs 2.5 crore was seized from a Sri Lanka-bound boat at Keelakarai and three persons were arrested on November 24.