Natural manganese ore is a kind of arsenic removal mineral. It is low-cost and widely available. In order to enhance its removal efficiency and adsorption quantity of arsenic, this paper adopted TiCl4 to modify natural manganese ore and optimized the conditions of modification. The results showed that the best modification condition was: TiCl4 at a concentration of 10 mg•L-1, dipping time of 18h, pH 3.05, reaction time of 60 min; under these conditions, the removal rates of As (Ⅲ) and As (Ⅴ) respectively reached 94.87% and 99.31%, much higher compared with natural manganese ore (82.95% and 77.93%). The saturated adsorption quantity of As (Ⅲ) and As (Ⅴ) reached 3.48 mg•g-1 and 3.27 mg•g-1, each increasing 1.25 mg•g-1 and 1.21 mg•g-1. The adsorption of As (Ⅲ) by modified manganese ore fits the Freundlich adsorption isotherm, while As (Ⅴ) fits the Langmuir adsorption isotherm best.