[en] One of the most common environmental problems of recent decades is the eutrophication of surface water and the associated algal bloom. As one of the approaches to eliminate this phenomenon, the use of biological methods, in particular biological preparations from barley straw, is considered. In this work presents the results of laboratory modeling of the effect of 1 and 2% (v/v) of barley straw (Hordeum vulgare L.) extract on the development of unicellular algae (Chlorella vulgaris Beijerinck). The alhistatic effect was evaluated by the parameters of algae growth, which were measured using the spectrophotometric and fluorescent methods. The parameters were measured at 0, 7, 14 and 21 days. The addition of barley straw extract reduced algae growth, both with the addition of 1% and 2% concentration. A two-day toxicity test using Daphnia magna Straus showed no toxic effect of barley straw extract for both 1% and 2% concentration. (paper)