PRODUCTION OF LACTONE

PROBLEM TO BE SOLVED: To obtain a lactone simply, advantageously and technically easily by introducing a specific hydroxycarboxylic acid into a specific solvent under a specific condition, isolating by a distillation and then condensing. SOLUTION: This method for producing a lactone is provided by introducing (A) a monomer, an oligomer or a polymer state of an ω-hydroxycarboxylic acid (ester) of the formula: [O-(CH2 )n -CO]x OR1 [(n) is >=2; R1 is H or a 1-4C alkyl; (x) is an integer] into (C) a reaction medium which is inactive under a reaction condition, contains a dissolved catalyst (B) and has a sufficiently high boiling point under a condition at 150-300 deg.C and 0.1-1 mbar, and condensing the lactone of the formula which is isolated by distillation as a vapor state. As the component (B), it is preferable to use an acidic or a basic esterification catalyst. As the component (C), it is preferable to use a polyalkylene glycol diether, etc., having approximately 2,000 molecular weight, of which terminal groups are blocked with an alkyl group.