Abstract: Objective: The present study aimed to evaluate immunomodulatory effects of triple probiotics (Bifidobacterium lactis V9/Lactobacillus plantarum P-8/Lactobacillus casei Zhang) and fructo-oligosaccharide (BLLF) in mice and its mechanism. Methods: C57BL/6J mice received intragastric administration of distilled water (control group 0.1 mL/10 g) and different doses of BLLF (triple probiotics 0.01 mg/kg+fructo-oligosaccharide 0.1 g/kg, triple probiotics 0.02 mg/kg+fructo-oligosaccharide 0.1 g/kg, and triple probiotics 0.06 mg/kg+fructo-oligosaccharide 0.1 g/kg) 0.1 mL/10 g once daily for 30 days. The immunity of mice was evaluated by organ ratios. The function of cellular immunity, monocyte macrophage, humoral immunity, and NK cell activities of the mice were further evaluated. Results: Compared with the control group, low, medium and high dose BLLF showed no significant effects on body weights and organ ratios of the mice(P>0.05). BLLF showed no significant effects on ConA-induced mouse splenic lymphocyte proliferations(P>0.05). Medium and high dose BLLF significantly increased the delayed hypersensitivity induced by dinitrofluorobenzene in mice (P < 0.05). The macrophage carbon clearance function of mice in high dose BLLF group was significantly increased compared with the control group (P < 0.05). Medium and high dose BLLF significantly increased the mouse peritoneal macrophage phagocytosis of chicken red blood cells（P < 0.05). Medium and high dose BLLF significantly increased hemolytic activity and number of antibody producing cells in mice (P < 0.05). Medium and high dose BLLF significantly increased NK cell activities in mice (P < 0.05). Conclusions: BLLF exhibited potent immunomodulatory effects by increasing cellular immunity, humoral immunity, function of monocyte macrophage, and NK cell activity.