Ganoderma lucidum (Leyss. ex Fr.) Karst. is a valuable dietary supplement used worldwide for promoting health as well as a medicinal fungus for handling fatigue, immunological disorders, and cancer. Previous studies have revealed the immunoenhancing effect of G. lucidum and the polysaccharide extract, with potential involvement of gut microbiome. The oil of G. lucidum spores (GLSO)is one of the well-known G. lucidum-related products. However, there is little evidence supporting the immune promotion activity and the underlying mechanisms. The present study aims to investigate the immunoenhancing effect of GLSO in mice. GLSO enhanced macrophage phagocytosis and NK cell cytotoxicity of mice. Further microbiome and metabolomics studies showed that GLSO induced structural rearrangement of gut microbiota, mediating alterations in a wide range of metabolites. By clustering, multivariate and correlation analysis, the immunoenhancing effect of GLSO was found to be highly correlated with elevated abundance of several bacterial genera (Lactobacillus, Turicibacter and Romboutsia) and species (Lactobacillus_intestinalis and Lactobacillus_reuteri), and decreased level of Staphylococcus and Helicobacter, which resulted in the regulation of a range of key metabolites such as dopamine, prolyl-glutamine, pentahomomethionine, leucyl-glutamine, L-threonine, stearoylcarnitine, dolichyl β-D-glucosyl phosphate, etc. These results provide new insights into the understanding of the modulatory effect of GLSO on immune system.