In the paper, there are discussed results obtained while investigating rheological properties of yogurts with different ageing times. Three types of natural yogurts showing various fat contents (2.2–3.3%) were four times tested. The tests were performed on different days during the expiry periods of yoghurts. Each test of a yogurt sample lasted 713 s, and during this time, the following constant shearing rates were applied, one after another: 30, 50, 70, 100 and 150 s^-1. The time interval was 23 s, and it was possible to score 31 testing points in each measuring series during this time. Some rheological parameters were measured, and an attempt was made to describe them using a mathematical model. Next, the results obtained were analysed, and, on this basis, a range of optimal shearing rates was determined for yogurts showing different ageing times. Based on the experiments accomplished, it was found that the experimental data were the nearest to the curve η = f (t) in case of 29 experimental points. This fact is proved by the lowest value of the ‘CV’ variance coefficient and the highest value of the ‘R’ correlation coefficient within the whole range of the experiments carried out. In addition, it was stated the existence of a relationship between the value of a shearing rate and the structure of a medium under investigation.