There is an increasing consumer demand for natural products, particularly in the area of food or food additives. This has created some possibilities for the use of slowly absorbable and nonabsorbable sugars as substrates for lactic acid bacteria and as prebiotics for human nutrition. The human colon contains a high concentration of bacteria (10000000000000 per gram dry weight of colonic contents). Recent studies show that bifidobacteria and lactobacilli are among the common anaerobic bacteria in the human colonic microflora and may exert beneficial effects on the host. Dietary sugar source is the main factor affecting the multiplication of bifidobacteria in the human intestine. Consequently, the administration of nondigestible oligosaccharides such as raffinose, fructooligosaccharides, galactosyllactose, isomaltooligosaccharides, or transgalactosyloligosaccharied causes an increase in the number of endogenous bifidobacteria and some changes in lactic acid bacteria. In this paper prebiotics and theirs charasteristis were described as also criteria for selection and safety of prebiotics and substrates.