The article describes the study of biocompatibility and bioactivity of a cytostatic agent [5-[[4,6-bis(aziridin-1-yl)-1,3,5-triazin-2-yl]amino]-2,2-dimethyl-1,3-dioxan-5-yl]methanol (substance (a)). The compound was characterised by means of ¹H and ¹³C NMR spectroscopy, IR spectroscopy, mass spectrometry. Biomedicinal investigations included haemocompatibility studies (spontaneous haemolysis, platelet aggregation, plasma-coagulation haemostasis, binding with human serum albumin and DNA); determination of antioxidant properties (reaction with 2,2-diphenyl-1-picrylhydrazyl, photo-induced haemolysis, photodynamic properties, NO-radical uptake); genotoxicity, as well as cytotoxicity using HEK-293, A549, PA-1, T98G, SK-HEP-1, PANC-1 cell lines. The article shows two possible mechanisms of the cytostatic action of the substance (a): due to its antioxidant activity and the possibility of the formation of adducts with DNA.