Highly enantioselective aldol-type reaction between achiral ketene silyl acetals of acetic acid esters and achiral aldehydes is successfully carried out by the use of a chiral promoter, a combined use of chiral diamine coordinated tin (II) trifluoromethanesulfonate (tin (II) triflate) and tributyltin fluoride. The structure of this new promoter and the mechanism of the present asymmetric aldol-type reaction are discussed.