wherein either of A and B represents a methyl group and the rest represents a hydrogen atom, which comprises oxidizing a dimethyldecanedial represented by the general formula (I)
wherein either of A and B represents a methyl group and the rest represents a hydrogen atom. The present invention provides a dimethyldecanedial represented by the general formula (I). Furthermore, the present invention provides a process for producing a dimethyldecanedial represented by the general formula (I), comprising hydroformylating a diolefin represented by the general formula (III)
wherein either of A and B represents a methyl group and the The dimethyldecanedial of the present invention is useful as a raw material of production of the dimethyldecanedioic acid represented by the general formula (II). Furthermore, the polyester diol containing the dimethyldecanedioic acid as a dicarboxylic acid component, shows excellent resistance to hydrolysis and is useful as a raw material for producing high-performance polyurethanes.