Abstract—This paper presents the experimental results of rare earth element and yttrium (REY) biosorption in natural surface waters and groundwater in the presence of different concentrations of living and inactivated organotrophic bacteria (Curtobacterium sp., Ralstonia sp., Pseudomonas sp., Bacillus sp., Brevibacterium sp., Microbacterium sp.,) under different environmental pH conditions. We found that the biosorption process is mainly regulated by two factors: the pH of the aqueous solution and the species of bacteria. The acidity significantly affected the sorption capacity of bacteria for all of the studied strains. We found a decrease in REY sorption with an increase in pH due to lower absorption of REY on the cell walls of bacteria. The process of REY biosorption was more intensive in the living bacteria than inactivated microorganisms. At neutral pH values, all studied bacterial strains more actively adsorbed light REYs (lanthanum, praseodymium, and neodymium), in more acidic solutions (pH 2), an increase in Kd values for heavy REY (lutetium and europium) was observed. The effect of bacterial biomass concentration on REY biosorption was demonstrated. The REY sorption decreased with an increase in the concentration of the live and inactivated bacteria.