The growth behavior and acid production of Lactobacillus  casei -01 and Bifidobacterium bifidum Bb-12 in bio-yoghurt made with three different yoghurt starter cultures (YC- Fast 1, YC-380 and YC-180) were investigated. The titratable acidity was increased rapidly in yoghurt samples made with YC fast-1, compared wih the other yoghurt strains. The coagulation time was 3, 3.5 and 4 h for bio-yoghurt made with YC fast-1, YC-380 and YC-180 respectively. The total viable counts of L. casei and B. bifidum were the highest in bio- yoghurt  samples made with YC-180 at the end of fermentation period (4h). Effect of some techniques on the viability of probiotics bacteria was also studied. Microencapsulation of  probiotics, addition of heat  shocked  yoghurt  starter or nonviable K. lactis NRRL Y-8279 had an enhancement effect on the viability of probiotics. Microbiologically, all fresh and stored yoghurt  samples were free from coliform and molds & yeasts. Organoleptically, bi-yoghurt made with microencapsulated  bacteria or with the addition of nonviable cells had higher   scores for acceptability compared with the others.