A method for producing a hetero-type monodisperse polyethylene glycol represented by the formula, which comprises the following steps,,,, and: wherein, in the formula, a represents an integer of 6 to 12, Step: a step of carrying out a nucleophilic substitution reaction between a compound of the formula and a compound of the formula so as to satisfy the requirement of the expression to obtain a compound of the formula: wherein, in the formula, b represents an integer of 3 to 9, wherein, in the formula, L represents a mesyl group or a tosyl group, R 1 represents a trityl group or a benzyl group, and c represents an integer of 3 to 9, 6 ≤ b + c ≤ 12 wherein, in the formula, R 1 represents a trityl group or a benzyl group and a represents an integer of 6 to 12; Step: a step of carrying out Michael addition reaction of a compound of the formula to the compound of the formula obtained in the step under a temperature condition of 10°C or lower to obtain a compound of the formula, wherein, in the formula, R 2 represents a hydrocarbon group having 1 to 6 carbon atoms, wherein, in the formula, R 1 represents a trityl group or a benzyl group, R 2 represents a hydrocarbon group having 1 to 6 carbon atoms, and a represents an integer of 6 to 12; Step: a step of detritylating or debenzylating the compound of the formula obtained in the step to obtain a reaction product containing a compound of the formula, wherein, in the formula, R 2 represents a hydrocarbon group having 1 to 6 carbon atoms and a represents an integer of 6 to 12; Step: a step of purifying the compound of the formula from the reaction product obtained in the step; Step: a step of reacting the compound of the formula obtained in the step with phthalimide and performing dephthalimidation to obtain a compound of the formula, wherein, in the formula, R 2 represents a hydrocarbon group having 1 to 6 carbon atoms and a represents an integer of 6 to 12; and Step: a step of subjecting the compound of the formula obtained in the step to an acid hydrolysis treatment to obtain the compound represented by the formula. Step: a step of carrying out a nucleophilic substitution reaction between a compound of the formula and a compound of the formula so as to satisfy the requirement of the expression to obtain a compound of the formula: wherein, in the formula, b represents an integer of 3 to 9, wherein, in the formula, L represents a mesyl group or a tosyl group, R 1 represents a trityl group or a benzyl group, and c represents an integer of 3 to 9, 6 ≤ b + c ≤ 12 wherein, in the formula, R 1 represents a trityl group or a benzyl group and a represents an integer of 6 to 12; Step: a step of carrying out Michael addition reaction of a compound of the formula to the compound of the formula obtained in the step under a temperature condition of 10°C or lower to obtain a compound of the formula, wherein, in the formula, R 2 represents a hydrocarbon group having 1 to 6 carbon atoms, wherein, in the formula, R 1 represents a trityl group or a benzyl group, R 2 represents a hydrocarbon group having 1 to 6 carbon atoms, and a represents an integer of 6 to 12; Step: a step of detritylating or debenzylating the compound of the formula obtained in the step to obtain a reaction product containing a compound of the formula, wherein, in the formula, R 2 represents a hydrocarbon group having 1 to 6 carbon atoms and a represents an integer of 6 to 12; Step: a step of purifying the compound of the formula from the reaction product obtained in the step; Step: a step of reacting the compound of the formula obtained in the step with phthalimide and performing dephthalimidation to obtain a compound of the formula, wherein, in the formula, R 2 represents a hydrocarbon group having 1 to 6 carbon atoms and a represents an integer of 6 to 12; and Step: a step of subjecting the compound of the formula obtained in the step to an acid hydrolysis treatment to obtain the compound represented by the formula.