Mandayam Jeersannidhi Thirumalachar (22 September 1914 – 21 April 1999) was an Indian mycologist, microbiologist, plant pathologist and the co-founder of Jeersannidhi-Anderson Institute, California. He was the head of R&D at Hindustan Antibiotics Limited and a professor at Banaras Hindu University as well as the Central College of Bangalore. He was known for the development of antifungal antibiotics such as Hamycin, , , and and was an elected fellow of the Indian National Science Academy. The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards for his contributions to Medical Sciences in 1967.