The waste drum monitoring system based on HPGe detector was used to study its performance for the estimation of low amounts of plutonium in presence of high activity of 137Cs and 60Co. The counting was carried out by keeping amount of plutonium constant at 100 mg level and varying the count rate for the γ rays of 137Cs and 60Co. Present study has shown that the estimation of low amount of 239Pu in a waste drum can be carried out using 129 keV γ ray in the presence of 137Cs up to an activity level of 16 mCi and in the presence of 60Co up to an activity level of 8 mCi.