This research was conducted with the aim of studying the effect of oat flour addition on thernphysico-chemical and microbiological quality of probiotic low fat bio-yoghurts. The low fat bioyoghurtsrnwere prepared through mixing of liquid skimmed milk with oat flour, starter culture,rncorn starch stabilizer, skimmed milk powder and sugar according to the basic formulation forrnbio-yoghurt production. The effect of mixing of oat flour (8%, 12 % and 16%) and storage daysrn(7days, 14 days and 21days) on physico-chemical properties, microbiological qualities,rnproximate composition, and sensory qualities of the low fat bio-yoghurt has been studied. Thernoat flour (Avena sativa) variety had a nutritional composition of 5.62% moisture, 16.94%rnprotein, 6.12% fat, 1.82% ash, 4.94% crude fiber and 64.65% carbohydrate, and the skimmedrnmilk contained 0.31% fat, 3.51% protein and 0.86% ash. After fermentation, the proximaterncomposition of the control bio-yoghurt, and the 8% Oat flour,12% and 16% Oat flour added bioyoghurtsrnwas; moisture (86.66%, 76.01%, 72.82% and 66.09%), crude protein (3.05%, 6.30%,rn10.29% and 7.30%), crude fat (0.30%, 1.21%, 3.72% and 4.77%), crude fiber (0%, 4.03%,rn4.80% and 4.97%) and ash (0.61%, 0.99%, 1.31% and 1.30%); respectively. The physicochemicalrnresults of the control bio-yoghurt and 16% oat flour added bio-yoghurts was; pH (4.49rnand 4.55), syneresis (8.31% and 3.2%), TA (0.87% and 0.62%), App. Viscosity (0.66 pa.s andrn0.83 pa.s) and proteolysis (0.34 and 0.48); respectively.rnAddition of corn starch stabilizer had reduced the effect of spontaneous whey separation which,rnwas more significant (p