The present study was aimed at determining the efficacy and safety value of biotechnology produced fulvic acid (BFA) as a functional feed additive. Four BFA products produced by lactobacillus, bacillus, yeast and fermented BFA from above 3 mixed bacteria were added by a proportion of 1.5% to the conventional feed. Then the Sprague-Dawley rats were fed by normal feed and 4 different BFA feed for 4 weeks. It was observed that the counts of neutrophils, white blood cells, and monocytes was significantly decreased in the lactobacillus BFA group than the control group (P<0.05); neutrophil was reduced in bacillus BFA group than the control group significantly (P<0.05). Compared to the control group, total protein, albumin, and albumin/globulin ratio were increased in lactobacillus BFA group. The total bilirubin decreased significantly (P<0.05) both in lactobacillus BFA and Bacillus BFA group. Total weight gain and daily gain were increased in mixed fermentation BFA group significantly than the control group (P<0.05). For feed conversion rates in each group, the mixed fermentation BFA group had the highest feed efficiency, increased by 10.04% than the control group, followed by the yeast BFA group, with an increase by 4.14%. The mixed fermentation BFA group and lactobacillus fermentation BFA group had significantly reduced number of E. coli than the control group (P<0.05), while the number of lactobacilli was significantly increased than the control group (P<0.05). The thymus index was significantly higher in the mixed fermentation BFA group and Lactobacillus BFA group than the control group (P<0.05); while significant difference was seen in the spleen index between the mixed fermentation BFA group and the control group (P<0.01). Immu-serological indicators: the mixed fermentation group had significant increased serum levels of IgA, IgG, IgM and IL-2 compared with the control group (P<0.05); the Lactobacillus BFA group had obviously increased levels of IgA, IgG and IL-2 than the control group (P<0.05). It proves that the BFA has a positive effect on improving the health indicators and nutritional status, blood physiology and biochemistry, weight gain of rats, which can effectively promote the growth of animals and raise feed reward. It results in improving gut microbiota, promoting the digestion and absorption of nutrients, which significantly improved weight gain rate and the quality of external fur. It was suggested that BFA has a positive and effective effect on improving the nutrition of rats and promoting their healthy growth.