To develop effective and powerful probiotics, Saccharomyces cerevisiae strains producing cellulolytic enzymes were genetically engineered. Two plasmids were constructed in which the carboxymethyl cellulase (CMCase) gene of Clostridium thermocellum was connected in frame with GAPDH or ADH1 promoter. The resultant plasmids were transformed into various S. cerevisiae host cells, and the expression level and secretion efficiency of the CMCase were examined. The difference in genetic background of host strains did affect significantly the cell growth and expression and secretion levels of CMCase. Irrespective of the nature of the host cells, the ADH1 promoter-employing plasmid showed a greater expression level and plasmid stability than the GAPDH promoter-based plasmid. By the optimal host-vector system, S. cerevisiae SEY2102 harboring pVT-CT1 plasmid (ADH1 promoter), the highest expression level of 277 unit CMCase/L was obtained.