The configuration of the diastereoisomers, (Ia) and (Ib), of (α-methylbenzyl) succinic acid was determined by preparing them by the cis-reduction of cis- and trans-(α-methylbenzylidene) succinic acid, (IIa) and (IIb). It was also found that the Schwenk-Papa reduction of (IIa) and (IIb) proceeded stereospecifically and cis-addition of hydrogen to the double bond was observed. This stereospecificity of the reduction was further confirmed in other cases.