Both treatments and leaching tests of an Mg slag sample containing F of 2.15% from an Mg factory in northwest China were conducted in the present study, focusing on problems of F pollutions. By treating at 1000-1200°C in a muffle furnace, F leaching was decreased to a minimum level of 0.49-2.85 mg/l from the Mg slag with an original F leaching of 13.9 mg/l. The F leaching values increased to 4.83-95.5 mg/l, while treating the slag samples in a vacuum furnace. The treatments of Mg slag may thus be carried out in oxidizing atmosphere and under 1200°C to minimize fluorine pollutions and to improve environmental performances of the Pidgeon process.