Robert Kenneth Callow, FRS (15 February 1901 – 1983) was a British biochemist. He worked at the National Institute for Medical Research (NIMR, Medical Research Council) in Hampstead and Mill Hill, where his work on steroids included contributions to the isolation and characterisation of vitamin D, and the synthesis of cortisone from naturally occurring steroids. After he retired from the NIMR in 1966 he worked on insect pheromones at Rothamsted Experimental Station (now Rothamsted Research) until 1971.