Cereal-based fermented beverages like boza are known functional and probiotic foods. Boza is manufactured by yeast and lactic acid bacteria fermentation of only ones or mixture of various cereals. In this research, the effects of sugar, different microorganisms and inoculum ratios on physicochemical, nutritional and sensory characteristics of oat based boza were investigated. For this purpose, oat based boza production was carried out by 3 different of inoculation rates (0, 3 and 5%) of 3 starter cultures (Pediococcus damnosus 2.6, Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus). The usage aim of Pediococcus damnosus 2.6 and yoghurt starter cultures was for the production of exopolysaccharide and lactic acid. As a result of using mixed culture and rising inoculation rates stimulated fermentation activity in formulation of boza. Thus, the amount of total solid matter was reduced and increased the contents of ash, protein and mineral matter of oat boza samples. Although the lowest viscosity was determined in Pediococcus damnosus 2.6 inoculation, the most uniform texture was provided. Raw oat had unpleasant odor and flavor but fermentation enhanced sensorial properties of oats. The highest overall acceptance score was observed in oat boza with 3% of yoghurt starter cultures.