Effects of S. cerevisiae on immune parameters of the L. vannamei after 14 days of S .cerevisiae feeding were evaluated in this study. For this purpose a total of 300 pieces of shrimp with an average weight of 30 to 35 grams were selected from a pool shrimp Abadan CHOEBDEH. After making sure the health, absence of necrosis on the surface of the body, cuts antenna, shrimp were transferred to the center of BANDAR IMAM Research Station. Adaptation was carried out for 3-5 days. After the adaptation, shrimps were screened for virus (WSSV, TSV, MBV, HPV, YHV, BP, IHHNV and IMNV) and vibrio bacteria. After screening shrimps divided to two groups with three replication (including 50 pieces of shrimp in triplicate). The experimental diet has the commercial shrimp composition, but 2 g of S. cerevisiae substituted 2 g of fish meal. Shrimp of first group (T1) for 14 days with food containing nutritional yeast and shrimp in second group (T2) were fed with normal diet without yeast. After 14 days Immune Factors and survival rates in both groups were evaluated. The results showed that the relative survival rate between the two groups showed no significant difference. But Immune Factors (THC, TPP, PO, POD and SOD) in the treatment fed yeast (T1) compared to control treatment (T2) showed a significant increase. In conclusion these results suggest that the increased survival rate and resistance of shrimp after S. cerevisiae consumption occurs through immune modifications, such as increases in THC, TPP, SOD, SOP and PO activity
