The effect of lactic acid probiotic bacteria (Lactobacillus acidophilus LA 5 and Bifidobacterium bifidum BB 12) was determined on the storage stability of acid curd cheeses known as tvarogs. The tvarogs were sensory assessed, the content of water and fat therein was determined, the titratable acidity and pH value thereof were measured, and the whey syneresis was determined. The samples of cheeses were also rheologically analyzed, i.e. their hardness was assessed using a double penetration test (TPA). In the starters and experimental products analyzed, the counts of mesophilic lactic streptococcus and probiotic strains were determined. The analysis of tvarogs was performed immediately after the tvarogs were manufactured and wrapped up, and, then, after they were stored for 3, 7, 14, and 21 days at a temperature of 5 ± 1 °C. The acid curd cheeses analyzed were characterized by appropriate sensory features and a normative acidity, water content, and fat contents. A statistically significant (p ≤ 0,05) increase was reported in the hardness of all the analysed cheeses and a statistically significant (p = 0.05) correlation was found between the water content in and the hardness of the tvarogs. Despite the decreasing number of LAB, L. acidophilus LA 5, and B. bifidum BB 12 strains, the cheeses analyzed were characterised by the recommended LAB and probiotic bacteria counts (not less than 10⁶ ÷ 10⁷ cfu·g^-1) during the entire period of storage. The probiotic strains impacted the sensory quality of acid curd cheeses. The cheese containing Bifidobacterium bifidum BB 12 strain was characterized by the best sensory quality, whereas the cheese with Lactobacillus acidophilus LA 5 bacteria – by the lowest sensory quality.