Kadayanallur is a third largest city and a municipality in Tirunelveli District in the Indian state of Tamil Nadu of India. The name Kadayanallur comes from "Kadayaleeswara", the name of the presiding deity of Kadayaleeswarar kovil, a Hindu temple located in Kadayanallur. It is famous for saral (drizzling), which occurs yearly from May to August. It is also known for its vast paddy and coconut fields. Most of the last generation of residents were farmers; however, many are now employed in various parts of India and in foreign countries such as the United States, Singapore, and the Persian Gulf.

The Indian Postal Service Pincode is 627751. The Telecom Code (BSNL) is 04633.