The investigations were conducted in Eastern Croatia on two sites during three vegetation years. Four sugar beet hybrids were included in the experiment, two tolerant and two sensitive to the pathogenic fungus Rhizoctonia solani Kühn. The experiments were set up according to a split - block scheme in 4 repetitions on two soil types, each in 24 different variants. Elements of the study were: A. Hybrid (A1 - tolerant to pathogenic fungi R. solani (Santino – Strube); A2 - tolerant to pathogenic fungi R. solani (Jadranka - KWS); A3 - sensitive to pathogenic fungi R. solani (Fred - Strubs); sensitive to pathogenic fungus R. solani (Terranova - KWS)); B. Application of microbiological preparation EM Aktiv (B1 - control; B2 - soil treatment (40 l / ha); B3 - soil treatment (30 l / ha) + foliar application (10 l / ha)) C. Nitrogen fertilization (C1 - based on soil analysis results; C2 - reduced by 30%)). The presence of the pathogenic fungus R. solani was confirmed using the so-called „fast method“ repeatedly for all 3 years on both soil types used in the experiment. The "fast method" is accepted worldwide and is included in the standard methods of demonstrating the presence of the pathogenic fungus R. solani in plants (STRUBE - DIECKMANN; Alert LFTM). Also, R. solani was confirmed through the isolation of pathogens using selective media as Potato dextrose agar and Corn meal agar. The microbiological preparation EM Aktiv contains P. fluorescens, B. megaterium and B. subtilis. Because of their exudats, these beneficial bacteria have a microbicidal effect on pathogenic fungi in the soil - causative agents of sugar beet root rot. Furthermore, the microbiological composition contains nitrogenous bacteria A. chroococcum and A. brasilense. In variants where biopreparation was applied, either solely applied into the soil or applied into the soil and foliar, compared to the control variant, a lower average percentage of infected and failed plants, potassium, sodium and alpha-amino nitrogen and sugar content was obtained, as well as higher root yield, sugar content, percentage of sugar utilization in beet root and pure sugar yield. Tolerant hybrids achieved a lower average percentage of infected and failed plants, potassium, sodium and alpha-amino nitrogen and sugar content than sensitive hybrids, as well as higher root yield, sugar content, sugar beet yield and pure sugar yield. However, significantly higher is the difference between the control variants and variants with biopreparation observing sensitive hybrids than it is on the variants with tolerant hybrids.