Poornam Viswanathan (14 November 1921 – 1 October 2008) was an Indian actor who predominantly appeared in Tamil films.
He went on to act in films such as Chithram, Varusham 16, Thillu Mullu, Keladi Kanmani, Moondram Pirai, Aasai, Mahanadhi and Varumaiyin Niram Sivappu.
He later moved to New Delhi for a few years, where he was part of the South Indian Troupe with dance and music critic Subbudu.
His portrayal of roles in plays scripted by Marina, such as Thanikuduthanam, Oor Vambu and Kaal Kattu, won him great acclaim.
He also starred in the Bollywood blockbuster Ek Duje Ke Liye (1981), in which he played the role of Kamal Hassan's strict father.