Abstract <p>The study investigates the effects of synthesis conditions on the physicochemical properties and biological activity of Beta zeolites. Specifically, it addresses the effects of the tetraethylammonium hydroxide (TEAOH) content in the reaction mixture on the crystallinity, particle size and morphology, textural properties, acidity, and hemolytic activity of the zeolites synthesized. Reducing the TEAOH content by factors of 2, 4, and 6 compared to the reference composition was found to lower the zeolite crystallinity, increase the mean particle size (from 240 to 515 nm), change the particle morphology, and reduce the concentration of acid sites (from 822 to 638 µmol/g). Hemolytic activity tests demonstrated that the zeolite toxicity for human erythrocytes increased with a reduction in the TEAOH content.</p>