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An eight-week feeding trial was conducted to evaluate the effects of different dietary probiotic supplements in juvenile whiteleg shrimp, <i>Litopenaeus vannamei</i>. A basal control diet without probiotics (CON), and five other diets by supplementing <i>Bacillus subtilis</i> at 10⁷ CFU/g diet (BS₇), <i>B. subtilis</i> (BS₈), <i>Pediococcus pentosaceus</i> (PP₈), and <i>Lactococcus lactis</i> (LL₈) at 10⁸ CFU/g diet, and oxytetracycline (OTC) at 4 g/kg diet were used. Whiteleg shrimp with initial body weights of 1.41 &#177; 0.05 g (mean &#177; SD) were fed with these diets. Growth of shrimp fed BS₈ and LL₈ diets was significantly higher than those of shrimp fed the CON diet (<i>p</i> &lt; 0.05). Superoxide dismutase activity in shrimp fed PP₈ and LL₈ diets was significantly higher than that of shrimp fed the CON diet (<i>p</i> &lt; 0.05). Lysozyme activity of shrimp fed probiotics and OTC diets significantly improved compared to those on the CON diet (<i>p</i> &lt; 0.05). The intestinal histology showed healthier guts for shrimp fed the probiotic diets (<i>p</i> &lt; 0.05). Immune-related gene expression in shrimp fed BS₈, PP₈ and LL₈ diets was recorded as significantly higher than that of shrimp fed CON and OTC diets (<i>p</i> &lt; 0.05). Also, results of the challenge test for 7 days and the digestive enzyme activity of shrimp fed BS₈, PP₈, and LL₈ were significantly improved compared to those on the CON diet (<i>p</i> &lt; 0.05). Therefore, these results indicated that <i>L. lactis</i> at 10⁸ CFU/g could be an ideal probiotic for whiteleg shrimp, and also <i>B. subtilis</i> WB60 and <i>P. pentosaceus</i> at 10⁸ CFU/g could improve the growth, immunity, histology, gene expression, digestive enzyme activity, and disease resistance, while replacing antibiotics.