The objective of the research study was to determine the effect of technological processes, such as freezing, pasteurization, lyophilisation, production of juice and preserve, on the content of bioactive substances in bilberry fruits. The fresh bilberry fruits were characterized by a content of polyphenols amounting to 543 mg GAE/100 g on average, and this content determined their antioxidant activity (7.7 mmol of Trolox / 100 g of fruits). At the same time, the amount of ascorbic acid was 43.7 mg per 100 g of fresh fruits. The technological processes caused the content of bioactive compounds in the fruits analyzed to decrease. The lowest losses in total polyphenolic compounds and vitamin C were reported after the freezing process (18 and 11 %, respectively), whereas the highest losses in those compounds were determined during the production of juices (64 and 58 %, respectively). Moreover, the juices were characterized by a low antioxidant activity (1.94 mmol of Trolox / 100 g of product). The lyophilized fruits were characterized by the lowest antioxidant activity compared to the fresh fruits (with the process efficiency included). Therefore, the lyophilisation process is not a suitable method for the preservation of billberry fruits. Despite considerable losses in bioactive compounds during the preservation and processing, the bilberry products are a good source of those compounds, especially from the point of view of the seasonality of supply thereof.