Acid milk drinks (AMD), such as drinking yogurt and kefir, are popular throughout the world. Over time, instability of these drinks can occur by aggregation of protein particles and whey separation. The objectives of this research were to investigate physio-chemical properties of high protein AMDs and their stability over time. Micellar casein isolate (MCI) is a dairy powder that contains a high ratio of casein to whey proteins and is obtained by microfiltration of milk. The first phase of this research was to compare 2 types of milk powders: MCI and nonfat dry milk (NFDM) – to observe how the use of different dairy proteins impact gel strength and stability of the fermented products. Milk bases were prepared (n = 2) at 8% protein, heated to 85°C for 30 min, cooled, and inoculated with starter culture and incubated at 40°C to pH < 4.3. Acidification rates were measured during fermentation along with small amplitude oscillatory rheology (SAOR) measurements using a rheometer. After incubation for 14 h gels were sheared at high and low speeds for 60 s in a blender and rheology, particle size (Malvern Mastersizer 2000), and pH were measured immediately post-shear and at 4 weeks of ambient storage. Acidification was faster for MCI due to less buffering compared with NFDM. SAOR performed during fermentation revealed that gels produced from MCI had lower storage and loss moduli compared to samples made with NFDM. The time-dependent recovery of gel structure after shear was observed in both AMDs and neither products remained fluid throughout storage, although MCI had lower gel stiffness immediately after shearing and after 4 weeks of storage. The yield stress of sheared products was higher for samples made from NFDM compared with MCI. Protein aggregation as measured by particle size was greater in NFDM, likely due to the higher concentration of denatured whey proteins. In conclusion, the weaker gel produced by MCI makes it an interesting choice for high protein AMDs, though a hydrocolloid like pectin may still be needed for long-term stabilization of the beverage at ambient temperature.