Sivan Kailasavadivu (born 14 April 1957) is an Indian space scientist who served as the Secretary of the Department of Space and chairman of Indian Space Research Organisation and Space Commission. He has previously served as the Director of the Vikram Sarabhai Space Center and the Liquid Propulsion Systems Centre.

Sivan worked on the design and development of launch vehicles for Indian Space Research Organisation (ISRO). Sivan joined ISRO in 1982 to participate on the Polar Satellite Launch Vehicle (PSLV) Project. He was appointed as the director of ISRO’s Liquid Propulsion Systems Centre on 2 July 2014. He was conferred Doctor of Science (Honoris Causa) from Sathyabama University, Chennai in April 2014. On 1 June 2015, he became the Director of Vikram Sarabhai Space Centre.

Sivan was appointed the chief of ISRO in January 2018 and he assumed office on 15 January. Under his chairmanship, ISRO launched Chandrayaan 2, the second mission to the moon on 22 July 2019, of which Vikram lander and Pragyan (rover) crashed; the orbiter was not affected and is still orbiting the moon as of August 2023.

On 30 December 2020, his chairmanship was extended by a year to January 2022. His earlier tenure was up to January 2021.

On 25 January 2021, Central Vigilance Commission (CVC) has registered a complaint against Indian Space Research Organisation (ISRO) Chairman and Secretary, Department of Space (DoS), K Sivan, over allegations of irregularities in recruiting his son in ISRO’s Liquid Propulsion Systems Centre (LPSC) in Valiamala, Thiruvananthapuram, by bypassing norms.