The effect of freeze drying of yoghurt and addition of some additives on the physico-chemical, microbiological, texture, microstructure, and sensory quality of yoghurt was studied. Freeze drying of yoghurt had light effects on the viability of Streptococcus thermophilus and no effect on viability of Lactobacillus delbreuckii subsp. bulgaricus and rehydrated yoghurt. Addition of modi fi ed starch had a considerable protection effect on Streptococcus thermophilus during freeze drying process. Addition of whey protein concentrate produced different surface structures and caused porous and loos structure. The microstructure of the freeze-dried yoghurt forti fi ed with spirulina powder showed a coarse and a compact less porous structure in comparison with the freeze-dried yoghurt samples for- ti fi ed with whey protein concentrate. All Additives signi fi cantly decreased adhesiveness and signi fi cantly increased cohesiveness, springiness, gumminess, and chewiness in both fresh and rehydrated yoghurts.