Protein-polysaccharide fractions, PJ-3 and PJ-4, were prepared from mycelial culture filtrate of an insect-born fungus, Paecilomyces japonica DGUM 32001, and subjected to a flow cytometrical analysis for their vivo antitumor and immunomodulating activity in ICR mice. When i.p. injected once daily for semen days at 100 mg/kg, PJ-4 exerted a strong antitumor activity showing the growth inhibition ratio of 85.1% against i.p. implanted sarcoma 180 cells, while PJ-3 showed only a weak activity. Moreover, PJ-4 signiscantly increased the expression level of CD25 (IL-2R $alpha$-chain) as well as forward scatter (FSC) values of splenic CD8$^{8}$ T cells. It is also noteworthy that PJ-4 strongly induced the peritoneal exudate cells in the same experiment. In an in vitro study, PJ-4 slightly inhibited the growth of sarcoma 180 cells at the concentration of 50$mu$g/ml or higher. These results strongly suggest that PJ-4 might exert its antitumor activity through immunostimulation as well as direct inhibitory activity on the tumor cells.