To obtain a high-optical purity diol compound in high yield by asymmetric reduction of a diketone compound using an optically active oxazaborolidine complex prepared from a specific optically active amino alcohol and a borane.

This compound of formula III is obtained by asymmetric reduction of a 1,3-diketone compound of formula I (R1 and R2 are each a 1-4C alkyl, benzyl or phenethyl; R1 and R2 forms indan-2-yl as a whole; R3 and R4 are each a 1-4C alkyl or the like; and (n) is 2-4), e.g. 2,2-diacetylindan in the presence of an optically active oxazaborolidine complex prepared from an optically active amino alcohol of formula II [R5 to R7 are each H, a lower alkyl, (substituted) phenyl or the like; R8 and R9 are each H, a lower alkyl or lower alkoxy; (*) is an asymmetric carbon atom] (e.g. optically active 2-amino-3- trimethylsiloxyl,1-diphenylbutanol) and a borane (e.g. methylboron) at -20 to 100°C.