Radionuclide activity of low and intermediate radioactive waste drums must be assayed prior to disposal. Some drums can not be assessed by the γ nuclide analyzer because of technical difficulties, time and cost. One alternative method, the dose to curie conversion (DTC) method, is used to assay the radionuclide activity in the waste drum. The uncertainties - the voids in the drum, the chemical composition and density of the contained material and the source distribution in the drum - associated with the DTC method were evaluated by using MCNP-4C code. Dose rate was sensitive to the density of the waste and the source distribution in the drum. It was insensitive to the voids in the drum and the chemical composition of the waste. For more accurate assay, the density variation and the source distribution were considered. The results of this work show a decrease in the error ratio from -69% to -31% for the density variation method and from -52% to -33% for the source distribution method. Applying both methods, the error ratio of assessment was decreased from -69% to 9% when compared with the existing method. The results of verification for the improved method using the experimental results indicate that the error ratio of assessment was decreased from -54% to -12.7% when compared with the existing method.