The combined effect of green microalgae Chlorella vulgaris and siliceous organo-mineral fertilizer (analcite + peat (pH 5.8) in a ratio of 1 : 3) on the characteristics of growth, development, photosynthetic productivity, yield and fruit quality of sweet pepper (Capsicum annuum L., variety "Bieloziorka"), as well as microbiocenosis, allelopathic and agronomic characteristics of the soil was studied in pot experiments. The microalgae culture medium was applied in a volume of 10 mL per a pot (0.7 L) with sifted and sterilized gray podzolic soil. Plants were grown in a phytochamber under controlled conditions of light, temperature and soil moisture. The vitality of the pepper plants was assessed by morphometric growth characteristics (shoot height, stem diameter, leaf surface area, length of roots, shoot and root dry weights, quantity and weight of fruits), content of photosynthetic pigments in leaves, protective antioxidants (carotenoids, flavonoids and anthocyanins) in fruits. At the end of the experiment, the content of phenolics, electric conductivity, redox potential, pH, the content of NH4+, NO3- and HCO3- in the soil solution were determined. A synergistic enhancement of the positive effect of microalgae and siliceous organo-mineral fertilizer on the growth, development, productivity and yield quality of sweet peppers has been established. The combined application of chlorella culture medium with siliceous organo-mineral fertilizer more effectively improved agronomic and allelopathic characteristics of the soil, stimulated the development of agronomically useful ecological and trophic groups of microorganisms, the intensity of mineralization and transformation of organic matter compared to control and treatments in which microalgae or fertilizer were applied separately.