The present study was conducted to clarify the effects of Lactobacillus salivarius (LS) ATCC 11741 and pectin (PE) on growth performance, digestive enzymes activity, gut microbiota composition, immune parameters, antioxidant defense as well as disease resistance against Aeromonas hydrophila in narrow-clawed crayfish, Postantacus leptodactylus. During 18 weeks trial feeding, 525 narrow-clawed crayfish juvenile (8.07 ± 0.1 g) fed with seven experimental diets including control (basal diet), LS1 (1 × 107 CFU/g), LS2 (1 × 109 CFU/g), PE1 (5 g/kg), PE2 (10 g/kg), LS1PE1 (1 × 107 CFU/g +5 g/kg), and LS2PE2 (1 × 109 CFU/g +10 g/kg). After 18 weeks, growth parameters (final weight, weight gain, and specific growth rate) and feed conversion rate were significantly improved in all treatments (P < 0.05). Besides, diets incorporated with LS1PE1 and LS2PE2 significantly increased the activity of amylase and protease enzymes compared to LS1, LS2, and control groups (P < 0.05). Microbiological analyses revealed that the total heterotrophic bacteria count (TVC) and lactic acid bacteria (LAB) of narrow-clawed crayfish fed diets containing LS1, LS2, LS1PE1, and LS2PE2 were higher than control group. The highest total haemocyte count (THC), large-granular (LGC) and semigranular cells (SGC) count, and hyaline count (HC) was obtained in LS1PE1 (P < 0.05). Similarly, higher immunity activity (lysozyme (LYZ), phenoloxidase (PO), nitroxidesynthetase (NOs), and alkaline phosphatase (AKP)) observed in the LS1PE1 treatment compared to the control group (P < 0.05). The glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity remarkably enhanced in LS1PE1 and LS2PE2, while malondialdehyde (MDA) content reduced in these two treatments. In addition, specimens belonging to LS1, LS2, PE2, LS1PE1, and LS2PE2 groups presented higher resistance against A. hydrophila compared to the control group. In conclusion, feeding narrow-clawed crayfish with synbiotic had higher efficiency on growth parameters, immunocompetence, and disease resistance compared to single consumption of prebiotics and probiotics.