Abstract: The optimal conditions of the Cd(Ⅱ)-Cadion 2B-Tween 40system have been studied.In the alkaline medium of NaOH,a red Cd(Ⅱ)-Cadion 2B-Tween 40 complex forms with e_510nm=9.80×10⁴ The K_a of Cadion 2B and Surface tension in the system was estimated.It was proved that Kwas increased and the reagent species with absorption maximum at 605nm formed.Using the dual-wave length method at 510—605nm the apparent molar absorptivity for cadmium measured was 2.60×10⁵ The molar ratio of cadmium to Cadion 2B is estimated to be 1:3 as estimated by the molar ratio method and continuous variation method.The Beer's law is obeyed in 0—6μg Cd/25ml.Using the proposed method with TEA,IDA and CIT masking mixture,the Cd content in rice samples was determined with satisfactory results.