The microbial transformation of sclareol, a tobacco constituent, by a soil bacterium JTS-162 was studied. Manool, manoyl oxide and a new compound; 14,15-dinorlabd-8(17)-en-13-one were isolated from the culture broth as transformation products. In the presence of metabolic inhibitors such as a,a'-dipyridyl, a compound; labda-8(17),14-dien-1 3/?,18-diol and two new compounds; 13/5hydroxylabda-8(17), 14-dien-18-al and 13/?-hydroxylabda-8(17),14-dien-18-oic acid were accumulated in the culture broth as transformation products. Based on the experiments with degradation sequence, the biotransformation pathway of sclareol by the bacterium was proposed. The microbial transformation of diterpenoids has not been studied so muchas that of monoterpenoids. Only the microbial conversion of abietic acid and its related compounds was studied in detail.1>2) In the previous paper,3) we reported the microbial transformation of cw-abienol [(12Z)-labda-12,14-diene], a major labdane of tobacco leaf wax. This was attempted to obtain new aroma compounds for tobacco flavoring by an unidentified soil bacterium, JTS-162. This microorganism first dehydrated cw-abienol at C-8 and C-17 positions and produced (12Z)-labda-8(1 7), 12,14-triene. This triene was oxidized stepwise at its a-methyl group at C-4 to give (12Z)-labda-8(17),12,14trien-18-ol and (12Z)-labda-8(17),12,14-trien-18-al. Next step of conversion was splitting of A-ring and resulted in 4, 18, 19-trinor-3,4-,s