A color developer for heat sensitive recording which comprises 0.5 to 5 parts by mass of 3-allyl-4-allyloxy-4'-hydroxydiphenylsulfone, 4-allyloxy-3'-allyl-4'-hydroxydiphenylsulfone or a mixture of these compounds per 100 parts by mass of 4-allyloxy-4'-hydroxydiphenylsulfone, a process for producing the color developer and a heat sensitive recording material comprising the color developer in the heat sensitive color forming layer. The color developer and the recording material suppress fog on the background and exhibit excellent color forming property and storage property of image portions.