This research studied the efficiency removal of iron and manganese in raw water of mixing tank in clarifier water process of Glow Energy Public Company Limited, which the contaminate of iron and manganese 4.0 mg/L and 0.4 mg/L, respectively with the jar test method. The fast mixing 70 rpm, slow mixing 20 rpm and 17 rpm, take each speed for 8 minutes. For the effect of coagulant, polyaluminium chloride which gives removal of iron and manganese have changed little. But make the particle to big size and sediment easily. And sodium hypochlorite as an oxidizing agent for the removal of iron and manganese and the optimum 7 mg/L of sodium hypochlorite, can provide effective removal of iron and manganese to high 88.21% and 44.46% respectively, And the effects of the amount of iron and manganese in raw water has resulted in iron removal efficiency is increased by the amount of iron and manganese in raw water but the manganese removal efficiency is inversely proportional to the amount of iron and manganese. Which used to improve the quality of raw water. To prevent the fouling of membrane of ultra filtration and reverse osmosis process