The potential for using a heterotrophic microorganism (Aspergillus niger) to depress magnesite from magnesite tailing has been assessed. The influence of metabolic activities produced by Aspergillus niger on the surface properties of magnesite tailings was studied. In this research studies of the adsorption of sodium oleate microflotation tests and FTIR spectroscopy analysis were carried out. it has also been demonstrated that a depressing effect can be obtained using both selected amino acid (Arginine, Asparagine and Methionine) and organic acid salts (potassium citrate and potassium oxalate). The mechanism of competition between a modifier reagent and sodium oleate was discussed.