The present study was carried out to reveal the effect of yeast cell wall preparation as an immunomodulator of the innate immune response. To evaluate its effect on chicken, yeast cell wall preparation (NutrifermTM) was administrated orally to 1-week-old broilers @ 0.4gm and 0.8gm per kg feed for 15 days and then switched back to control diet for 20 days. Similar number of birds was kept separately as control with normal feeding regime. Non-specific immunity was assessed in randomly selected treated and control birds at the end of the experimental feeding period ('0' day) by performing neutrophil, monocyte and lymphocyte functional assay in vitro. In both dose group super oxide anion production by neutrophil was increased gradually up to '10' day post treatment (DPT) and then decreased to '20' DPT. The increase was significant (P>0.5) compared to control birds. In vitro nitrite production by monocyte was found to be high in treated birds than control. In 0.4gm treatment group in vitro non-specific lymphocyte proliferation and IL-2 production was first increased and then decreased abruptly.