Disclosed are a heat-resistant SAN resin, a method of producing the same and a heat-resistant SAN resin composition comprising the same. More specifically, disclosed are a heat-resistant SAN resin produced using ingredients comprising 52 to 78% by weight of alpha-methylstyrene, 20 to 40% by weight of a vinyl cyanide compound and 2 to 8% by weight of hydroxyalkyl (meth)acrylate, a method of producing the same and a heat-resistant SAN resin composition comprising the same. Advantageously, provided are a heat-resistant SAN resin with maintained heat resistance, improved polymerization conversion rate and increased weight average molecular weight, a method of producing the same, and a heat-resistant SAN resin composition containing the same with excellent chemical resistance, superior mechanical properties and good balance between properties.