Abstract: A rapid sensitive and selective spectrophotometric method for the determination of total amount of the rare earth elements in the ferroalloy of containing rare earth silicon and magnesium has been developed. A purplish red complex which has ratio of RE to Arsenazo-Ⅲ to be 1:2 can be formed in the range of pH 1.2~2.1 in the ethanol aqueous solution (λ_max=648nm,λ₆₄₈=8.2×10⁴ mol^-1cm^-1). Beer's law is obeyed in the concentration range of 0 to 50μg/25ml.The interference of Fe(Ⅲ) can be covered with EDTA.