A method for fermenting Rosa sterilis var. leioclada includes providing a fruit sample of Rosa sterilis var. leioclada. A Lactobacillus casei strain, a Bifidobacterium longum strain and a Saccharomyces cerevisiae strain are mixed in a cell number ratio of 0.3-1:0.2-0.9:1-1.8 to form a microbial mixture. The fruit sample of Rosa sterilis var. leioclada is then fermented by the microbial mixture at 22-33° C. for 6-15 days to obtain a fermented juice. A total concentration of the Lactobacillus casei strain, the Bifidobacterium longum strain and the Saccharomyces cerevisiae strain in the mixture solution containing the microbial mixture and the fruit sample of Rosa sterilis var. leioclada is between 1.5×107 and 3.5×107 CFU/mL.
