Vaikathashtami (Vaikkathashtami) is a popular 12-day temple festival of Kerala, South India, falling between mid November and mid December. It is the annual festival of the Vaikom Mahadeva temple, situated on the banks of the Vembanad lake at Vaikom (Vaikkom), in the district of Kottayam. The festival offers a rich cultural fare in the form of dance recitals and music concerts.

During the festival, the idol of Lord Siva is taken out on a grand procession round the town on the seventh day of the festival. This procession is joined by another grand procession from the Muruka temple of Udayanapuram, situated nearby.

The Vaikom Mahadeva temple has also historical importance in that an agitation (Vaikkom Satyagraha) to remove some of the inequalities in worshipping rights was initiated here.