The usage of magnesite strictly depends on its impurities. CaCO3 is the major impurity in magnesite ores. The amount of CaCO3 should be less than 1% for the quality and economical use of magnesite ores. Some magnesite ores in Turkey cannot be used due to high amount of CaCO3 (>= 3%). This study aims to investigate an alternative biotechnological method for decalcification of magnesite ores by using a microorganism (Lactococcus spp.). The amount of CaCO3 was reduced from 2.94% to 0.57%. This reduction improved the quality of magnesite ore by approximately 80.61%. The results showed that Lactococcus spp. can be used safely in industrial decalcification of magnesite ore as the microorganism has no pathogenic properties. (C) 2015 Published by Elsevier B.V.