Abstract: Objective: This study aimed at investigating the effect of immunostimulant administered at different times on the growth performance of whiteleg shrimp reared at different stocking densities. Materials and Methods: This study used a randomized complete block design (RCBD) with two factors. Factor A was administration times (7th, 14th, 21st and 28th days) and factor B was stocking densities (10 larvae/15 L, 15 larvae/15 L and 20 larvae/15 L). Data in terms of specific growth rate (SGR), feed efficiency (FE) and feed conversion ratio (FCR) were calculated and compared among treatments using Analysis of Variance (ANOVA), followed by Duncan's Multiple Range Test to find a significant difference among treatments. Results: The results showed that SGR, FE and FCR were significantly affected by stocking density and administration time, p<0.05. The highest specific growth rate was obtained from shrimp with a stocking density of 20 shrimps/15 L at the administration of the 7th day. While the best FE is in a stocking density of 15 shrimps/15 L given on the 21st day, then the best FCR was in a stocking density of 20 shrimps/15 L given on the 28th day. Conclusion: SGR, FE and FCR of white shrimp were significantly influenced by the administration time of immunostimulant (whole protein of Zoothamnium penaei ) and stocking densities.