Magnesite is a primary source of magnesium and its compounds. The major problem in its practical use are the impurities such as silicon, iron and calcium carbonate. Some magnesite ores in Turkey cannot be used due to a high amount of CaCO3 (3%). In this study, bacterial isolates from magnesite quarries in Mersin were tested by plate assay for their ability to decalcify magnesite. A bacterial strain producing the largest clear zones in the plate assay was identified as Pseudomonas oryzihabitans by 16S rDNA-PCR and applied to magnesite ore. It was found to be effective in decalcifying magnesite ore without significant concurrent dissolution of the magnesium carbonate.