S. Sivadas (born 19 February 1940) is an Indian children's writer in Malayalam.

He is the author of around 200 books which include popular science, contemporary ecology, short stories, novels and other fictional stories with an emphasis on scientific outlook.

Sivadas was born on 19 February 1940 in Ullala village near Vaikom in Kottayam district of Kerala.

He was the founder secretary of the Kottayam district committee of Kerala Sasthra Sahithya Parishad.

He also served as the chairman of Parishad's publication division, consulting editor of Sarvavijnanakosam, and the chairman of the Chemistry Post Graduate Board of Studies at Mahatma Gandhi University.