A. Sethumadhavan, popularly known as Sethu, is a Malayalam fictional writer. He has published more than 30 books.

He received the Kerala Sahitya Akademi Awards in 1982 and 1978 for his works "Pandavapuram" and "Pediswapnangal"; and Vayalar Award for "Adyalangal" in 2005. Sethu's other literary works include "Pandavapuram", "Velutha Koodarangal", "Pedi Swapnangal", "Thaliyola", "Kiratham", "Niyogam", "Sethuvinte Kathakal" and "Kaimudrakal".

He also served as the chairman of the South Indian Bank.