The invention discloses functional 
mulberry leaf oligosaccharide and a preparation method and application thereof. The method comprises the following steps that 1, dried mulberry leaves serve as raw materials, after crushing is conducted, 
degreasing is conducted by means of 
petroleum ether, and degreased 
mulberry leaf powder is obtained; 2, a 
mulberry leaf polysaccharide extracting solution is obtained by conducting 
water extraction on the degreased mulberry leaf 
powder; 3, 
hydrolase is added in the obtained mulberry leaf 
polysaccharide extracting solution, and 
oligosaccharide hydrolysate is obtained through enzymolysis; 4, 
ethanol is added in the 
oligosaccharide hydrolysate, unreacted mulberry leaf 
polysaccharide is subjected to 
alcohol precipitation, and a mulberry leaf oligosaccharide solution with polysaccharide removed is obtained; 5, 
saccharomyces cerevisiae is added in the mulberry leaf oligosaccharide solution with the polysaccharide removed, 
fermentation is conducted to removemonosaccharide, and finally the functional mulberry leaf oligosaccharide is obtained. Accordingly, 
alcohol precipitation is utilized for removing the polysaccharide, microbial 
fermentation is utilized for removing the 
monosaccharide, the mulberry leaf oligosaccharide separation and purification process is simplified, the functional mulberry leaf oligosaccharide has better economical efficiency and environmental friendliness, and the obtained mulberry leaf oligosaccharide has the physiological 
efficacy of promoting proliferation of intestinal 
beneficial bacteria and inhibiting growth of harmful 
bacteria.