The approximate rate and stoichiometry of the reaction of excess di-s-butoxyborane with selected organic compounds containing representative functional groups under standardized conditions (tetrahydrofuran, $25^{circ}C)$ were examined in order to define the characteristics of the reagent for selective reductions. And the catalytic effect of lithium tetra-s-butoxyborate on the reaction of di-s-butoxyborane was also studied in order to increase the utility of this reducing system. Di-s-butoxyborane reacts only with simple aldehydes. However the addition of 2.5 mole % of lithium tetra-s-butoxyborate shows the tremendous rate enhancement of reaction for aldehydes, ketones, anhydrides, acid chlorides, lactones, and epoxides. This catalytic effect is assumed to in situ formation of lithium trialkoxyborohydride.