The root endophyte Serendipita indica colonizes the roots of many mono- and dicotyledonous plants. Its positive effects include increasing plant growth and tolerances against biotic and abiotic stress factors. In this work, the growth-enhancing potential of S. indica on soybeans and the effect on the plant pathogen Sclerotinia sclerotiorum (Scl) was tested. For this purpose, soybeans were inoculated directly with S. indica in the greenhouse and infected with S. sclerotiorum by inflorescence inoculation. The plants were watered with a nutrient solution with and without phosphorous (P). In addition, S. indica and the Trichoderma strain T39 were tested for their growth-inhibiting potential against S. sclerotiorum in a dual culture system. Significant effects due to root colonization with S. indica could be seen in the root and shoot dry weight at +P+S. indica. +P +S. indica+Scl tend to have an inhibitory effect on S. sclerotiorum infestation, while -P+S. indica+Scl resulted the greatest infestation. The dual culture system showed no direct inhibitory effect of S. indica on S. sclerotiorum. No influence of S. indica on root and plant length could be detected. In summary, S. indica has potential for biomass increase and as a control agent against S. sclerotiorum. Based on this study it can be assumed that S. indica has no direct effects on S. sclerotiorum. The potential to reduce S. sclerotiorum via should be elucidated in further studies.