Abstract: Direct potentiometric method with ion selective electrode (ISE) was used in the determination of ammonia nitrogen in waste water.Ammonia in the sample solution was liberated by adding an alkali solution of EDTA and expelled from the sample solution by air-blowing with a micro air-pump.The liberated ammonia was absorbed in dil.H2SO4 and its potential measured with an ammonia gas sensitized ISE.The rate of liberation of ammonia from the sample solution achieved to values of 90%.Recovery of the method was tested by the standard addition method,and the results obtained were in the range of 60.0%-98.8%.RSD (n=8) found was less than 5%.Detection limit (3S) found was 0.008 mg·L-1,and the upper limit of determination was 350 mg·L-1.