Abstract Beta-glucans have been considered as potential growth promoters due to modifying the immune system. The trial objective was to study the efficacy of beta-glucan on lymphocyte viability and plasma IL-18 of weaning piglets. Four experimental groups with the following trial design were included in the study: control group A without beta-glucan, group B, C and D with 100, 250 and 500 mg/kg of beta-glucan, respectively. Blood samples of 6 piglets per group were taken on day 7 and 21. Lymphocytes were separated with density gradient centrifugation. WST-1 assay was used to determine lymphocyte viability and ELISA to quantify plasma IL-18. The beta-glucan preparation had an elevating effect on lymphocyte viability in doses of 100 mg/kg on day 7 and in doses of 250 mg/kg and 500 mg/kg on day 21. IL-18 showed a slight increase on day 21 in all trial groups in comparison to the control. It can be concluded, that yeast beta-glucan might be used as an immunomodulating agent.