A new catalytic spectrophotometric method for the determination of trace amount of Mn(II) has been developed. The method is based on the oxidation of thionine by potassium periodate in the presence of nitrilo triaceticacid as an activator and amphoteric surfactant dodecyl dimethylamino acetic acid(DDMAA) as enhancing agent. Dodecye dimethylamino acetic acid (DDMAA) micelles accelerate the reaction and hence increase the sensitivity and selectivity of the determination of Mn(II) compared to reactions taking place in an aqueous medium. The mechanism of related reaction has been discussed. The sensitivity is increased by 7.1 times in the presence of the DDMAA than that in the absence of the DDMAA. The linear ranges of determination are 0-60 ng.(25 mL)-1, the relative standard deviation is 2% (n = 11). The method can be used for the determination of Mn(II) in aluminium alloy and water samples.