One of the most interesting fermented milk products with functional properties is acidophilus milk. It is well known that the nutritional value, therapeutic properties, and rheological characteristics of these products can be enhanced by incorporating various supplements. The objective of this study was to investigate the duration of fermentation and the change in pH value and acidity during 14 days of storage in supplemented acidophilus milk. The samples of milk with added honey (1% w/w) were additionally supplemented with whey protein isolates of cow origin at 0.5 % (w/w) and 1.5% (w/w) concentrations, or with whey protein isolates of goat origin at 0.5% (w/w) or 1.5% (w/w). A lyophilised bacterial culture of Lactobacillus acidophilus (LA-5) was used for direct inoculation into milk. So, five different acidophilus milks were prepared. According to the research results, the endpoint of fermentation was reached in intervals of 7 to 13 hours. The time required to target a pH of 4.60±0.05 was shortened by 38% with the addition of 1.5 % (w/w) whey protein isolate of cow origin. On the 14th day of storage, decreases in pH values were observed in every sample of prepared acidophilus milk. During storage, there were no significant changes in the lactic acid content in prepared supplemented acidophilic milks, except for the sample with added 1.5 % (w/w) whey protein isolate of goat origin. This supplemented acidophilus milk showed an increase in lactic acid content and a statistically significant difference (p<0.05) compared to the other samples, as well as the results at the 1^st and 7^th storage days. Compared to other published results, the prepared supplemented acidophilic milks showed fair stability of pH and lactic acid during 14 days of storage.