Kadaiyar (also spelled Kadayar) is a subcaste of Devendrakula Velalar an agricultural community found in the Indian state of Tamil Nadu and Sri Lanka. They are also known as Kadaisiyar.
Kadaiyar is derived from the Tamil word kaṭai meaning "low" or "least" and the honorific suffix -yar denoting people. The name might also be derived from kaṭai meaning "to mash" or "to grind" in reference to their traditional occupation as lime burners. In colonial records are they known as Kaddeas, a corruption of Kadaiyars.
The Kadaiyars belong traditionally to the Marutham Sangam landscape. They are mentioned in Puram as involved in agriculture.
They were one of the earliest Tamils to convert to Roman Catholicism along with the Paravars under Francis Xavier.
As of 2017[update], the Kadaiyar were a listed as a Scheduled Caste in Tamil Nadu under India's system of positive discrimination.