Kadayanallur (Tamil: கடையநல்லூர்) is a second largest city and a Ist Grade Municipal town municipality in Tirunelveli District in the Indian state of Tamil Nadu of India.

The most important commodities such as Handloom clothes, matches also fiber and mud-pots are being manufactured in the town.

The name Kadayanallur comes from "Kadayaleeswara", the name of the presiding deity of Kadayaleeswarar kovil, a Hindu temple located in Kadayanallur. It is located in the foothills of the Western Ghats near the Courtallam Waterfall and Tenkasi. It is famous for saaral (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 nearest airport is at Madurai, nearest international airport at Thiruvananthapuram then Kochin and a rail service (converted to broad gauge in 2004 2005), served by Southern Railway (India) is also available.