The need to expand the raw material base for obtaining flavonoids is due to the wide spectrum of their biological activity. The purpose of this work is to study the biological activity of a complex of bioflavonoids, quercetin and rutin on specific enzyme biotest systems in vitro. The objects of the study were: a complex of bioflavonoids from fat-free sea buckthorn meal Hippophae rhamnoides L. and individual flavonoids rutin and quercetin isolated from it. The study was carried out by methods of detecting the biological activity of substances using specific enzyme biotest systems in vitro. It was revealed that rutin and a complex of bioflavonoids have antioxidant properties – the rate of glutathione reductase reaction increased by 64 and 51% of control, respectively, and catalase – by 15%. Quercetin exhibits antimicrobial activity and also reduces the rate of the enzymatic iNOS reaction by 24% of the control, which indicates the anti-inflammatory properties of this sample. Rutin and a complex of bioflavonoids from sea buckthorn meal increased the iNOS reaction rate by 14 and 28%, respectively, which indicates the immunostimulating properties of these samples. In the course of a microbiological study, it was found that all samples have weak bacteriostatic activity against gram-positive and gram-negative bacteria Staphylococcus aureus ATCC 6538 (209-P) and Pseudomonas aeruginosa ATCC 9027. Fungistatic activity was confirmed against the yeast-like fungi Candida albicans ATCC 10231 of quercetin and the complex. The results obtained make it possible to consider a complex of bioflavonoids, quercetin and rutin as promising active substances in antioxidant, antimicrobial, fungistatic and anti-inflammatory drugs.