Abstract: This study was conducted to determine the effects of supplemental LP20 on growth performance and immune response of postlarvae (PL) and juvenile stages of white leg shrimp, Litopenaeus vannamei. The LP20 contains 20% heat-killed Lactobacillus plantarum strain L-137 (HK L-137) and 80% dextrin in dried-weight basis. The study was conducted for two phases: Phase 1 (hatchery stage- PL1 to PL15) was carried out indoor with four treatments by supplementation of LP20 at 0.0 g (marked as LP20-0.0), 0.5 g (LP20-0.5) and 1.0 g (LP20-1.0) LP20 kg-1 of feed to the basal diet.