Chloride in manganese ore adversely affects mineral extraction. The mechanisms and the factors that influence an alkali pretreatment to removal chlorine from manganese ore were explored to eliminate hazards posed by chlorine during the electrolysis of manganese. The results showed that sodium carbonate, when used as an alkaline additive, promoted the dissolution of insoluble chloride, enhanced the migration of chloride ions, and effectively stabilized Mn~(2+). The optimal conditions were a sodium carbonate concentration of 0.45 mol·L~(-1), a liquid-solid ratio of 5:1 mL ·g~(-1), a reaction time of 1 h, and a temperature of 25°C. The chlorine removal efficiency was greater than 95%, and the ore grade(Mn) was increased by 2.7%. The mechanisms and the factors that influence that alkali pretreatment to remove chlorine from manganese ore were explored to eliminate hazards posed by chlorine during the electrolysis of manganese. The results showed that sodium carbonate, when used as an alkaline additive, promoted the dissolution of insoluble chloride, enhanced the migration of chloride ions, and effectively stabilized Mn 2+. The optimal conditions were a sodium carbonate concentration of 0.45 mol·L -1, a liquid-solid a reaction time of 1 h, and a temperature of 25 ° C. The chlorine removal efficiency was greater than 95%, and the ore grade (Mn) was increased by 2.7 %.