Background: Beta-glucan has been frequently used in laboratory trials as an immunomodulator in both in vivo and in vitro studies, but the effective dose for measuring its performance has not been established. Like other immunomodulators, researchers must establish the right dose of beta-glucan in their laboratory experiments for the purpose of testing substances as immunomodulators without achieving false-positive or –negative results. This study aimed to determine the optimum dose of beta-glucan to induce cytokine production by peripheral blood mononuclear cells (PBMCs) in vitro. Subjects and Method: This was a laboratory experimental study. This study measured the production of two cytokines, including interferon gamma (IFN-γ) and interleukin 12 (IL-12), from the isolated PBMCs of healthy subjects. The doses of beta-glucan used as immunomodulator included 1, 5, 10, 20, and 50 μg/ml. Beta-glucan was added to the PBMC culture medium, and the PBMCs were cultured for 6 days. On the sixth day, the supernatant was harvested and the cytokine production was analyzed using sandwich enzyme-linked immunosorbent assay (ELISA). Cytokines were also analyzed using the human IFN-γ ELISA kit and the human IL-12 ELISA kit, and data analysis was performed by one-way ANOVA. Results: IFN-γ levels were found to be increased in the group treated with 5 μg/ml beta-glucan. The highest IFN-γ levels (70.0 pg/ml) were observed in the group treated with 10 μg/ml beta-glucan. The production of IL-12 increased sharply in the group treated with5 μg/ml beta-glucan but decreased in the group treated with 10 μg/ml beta-glucan. The mean cytokine levels of the beta-glucan group were found to be significantly different from those of the control group (p=0.001). One-way ANOVA revealed that the highest IL-12 production (77.2 pg/ml) occurred at a dose of 5 μg/ml beta-glucan. This average value was significantly different from the average production of IL-12 in the control group (p=0.001). Conclusion: The optimum dose of beta-glucan for stimulating PBMCs to produce IFN-γ in vitro was 10 μg/ml, while for the production of IL-12, the dose was 5 μg/ml. Both cytokines can be measured within 6 days of cell culture. Keywords: beta-glucan, immunomodulator, cytokines Correspondence: Meira Erawati. Faculty of Medicine, Diponegoro University. Jl. Prof. Soedarto, S.H, Tembalang, Semarang, Indonesia. Email: meiraerawati@gmail.com. Mobile: +62-81915339685 Indonesian Journal of Medicine (2020), 5(2): 170-177 https://doi.org/10.26911/theijmed.2020.05.02.12