Abstract: A new catalytic spectrophotometric method for the determination of trace amount of Mn(∏) has been developed. The method is based on the oxidation of fuchsin acid with potassium periodate in the presence of nitrilo triaceticacid as an activator and dodecyl dimethylamino acetic acid (DDMAA) as a sensitizer. The sensitivity is increased by 7 times(the rage 1.2～ 2.4 μg/L) and 14 times(the rage 2.4～5.2 μg/L) than that in the absence of the DDMAA. The relative standard deviation was 2.0% for 4.0 μg/L Mn(∏)(11 replicates). The limit of detection for Mn is 1.4～10^-10 mg/L. The method has been succesfully applied to the determination of Mn in tea sample.