To provide a novel method for producing a reactive polyoxytrimethylene glycol having unsaturated bonds and expected to be an important compound as a reactive polymer resource capable of forming a cleaning agent for lithography, various solvents, or a raw material for medicinal and agricultural agents, a plasticizer, a raw material for resins and a coating film in a simple manufacturing process with good selectivity by using easily available and easily handled raw material.

This polyoxytrimethylene glycol is expressed by general formula (1): CH(-R1)=C(-R2)-CH2-[O-CH(-R1)-CH(-R2)CH2]n-OH (1) (wherein R1 and R2 express each H or methyl, but at least one of R1 and R2 expresses H; n expresses ≥1 integer). This method for producing the polyoxytrimethylene gylcol expressed by general formula (1) comprises self-reacting (met)allyl alcohol or crotyl alcohol.