Disclosed is a novel method for group III polarity growth on a sapphire substrate. Specifically disclosed is a method for producing a laminate wherein a group III nitride single crystal layer is laminated on a sapphire substrate by an MOCVD method. The method for producing a laminate comprises: a pretreatment step in which an oxygen source gas is supplied onto the sapphire substrate; a first growth step in which an initial single crystal layer that contains oxygen at a concentration of 5×1020 cm−3 or more but 5×1021 cm−3 or less is grown with a thickness of 3 nm or more but less than 15 nm by supplying the oxygen source gas onto the sapphire substrate together with a starting material gas for the growth of the group III nitride; and a second growth step in which a group III nitride single crystal layer that is reduced in the oxygen concentration in comparison to the initial single crystal layer is grown by supplying the starting material gas onto the initial single crystal layer without supplying the oxygen source thereto, or alternatively by supplying the oxygen source, together with the starting material gas, at a lower supply rate than that in the first growth step.