Background: The high content of fiber and macromolecular substances in mushroom residue limits its utilization potential. After we fermented seafood mushroom residue with microorganisms, we found that its palatability and utilization have been greatly improved.The purpose of this study was to investigate the effects of feed containing fermented seafood mushroom residue on the growth performance and rumen microorganisms of goats. Methods: Forty-eight Jianyang big-ear goats with similar weight and good health were selected and randomly divided into 4 groups with 12 goats in each group. The control group (C) was fed a basic diet, and the experimental group 1 (L), 2 (M), and 3 (H) were fed diets supplemented with 20%, 30% and 40% fermented seafood mushroom residue.Results: Incorporating 20% fermented mushroom residue significantly increased the average daily gain (ADG) and average daily feed intake (ADFI) and reduced feed to gain ratio (F/G). Incorporating 30% in the diet significantly increased both ADFI and F/G. Growth performance was reduced when greater than 30% fermented mushroom residue was added. The beta diversity of the rumen flora was significantly increased with the 20% fermented mushroom residue diet. The relative abundance of Veillonellaceae, Ruminococcaceae, and Prevotellaceae increased, and the KEGG pathways related to metabolism of cofactors and vitamins, lipid metabolism, and xenobiotics biodegradation and metabolism were enhanced. Forty-nine KEGG pathways significantly associated with ADG were identified. Twenty-six pathways, including protein kinases, mineral absorption, propanoate metabolism, and biosynthesis of unsaturated fatty acids, were positively correlated with ADG. The remaining pathways, including pathogenic Escherichia coli infection, phenylpropanoid biosynthesis, shigellosis, and cyanoamino acid metabolism, were negatively correlated with ADG.Conclusions: These results show that adding 20% fermented seafood mushroom residue can improve the growth performance of goats and have a positive effect on goat rumen microorganisms.