Polysaccharopeptide (PSP), from Coriolus versicolor, has been used as an adjuvant to chemotherapy, and has demonstrated anti-tumor and immunomodulating effects. However its mechanism remains unknown. To elucidate how PSP affects immune populations, we compared PSP treatments both with and without prior incubation in phytohaemagglutinin (PHA) – a process commonly used in immune population experimentation. We first standardised a capillary electrophoresis fingerprinting technique for PSP identification and characterisation [1]. We then established the proliferative capability of PSP on various immune populations in peripheral blood mononuclear cells, using flow cytometry, without prior PHA treatment. We report, for the first time, that, in the absence of PHA, PSP increases the proportion of monocytes, but not T-cells, B-cell or NK-cell subsets of PBMCs in vitro. We found that PSP treatment of PBMCs at 100 µg/ml significantly increased CD14+/CD16 monocytes. This increase in monocytes was confirmed using another antibody panel of CD14 and MHCII. This further supported the role of PSP in antigen presentation. Thus, stimulating monocyte/macrophage function with PSP could be an effective therapeutic intervention in targeting tumors. Future studies, investigating the cytokine profiles responsible for stimulating the monocyte/macrophage function and the role in receptor function, by blocking TLR2/6/4 and Dectin-1 to confirm their role in PSP stimulation, are warranted.