Mannan, the surface polysaccharide antigen of Saccharomyces cerevisiae was partially oxidized and conjugated to a protein carrier. Prepared conjugate was immunogenic in mice and re-injection elicited significant increase of anti-S. cerevisiae specific IgG and IgM serum antibodies. There was somewhat less increase in IgM serum antibodies. Serum distribution of IgG subclasses, especially IgG(2(a+b)):IgG(1) ratio throughout the immunization demonstrated effective Th1 predominance of immune response. Newly synthesized S. cerevisiae mannan conjugate could be considered as a perspective vaccine candidate for preventive immunomodulation treatment.