This study is an attempt to develop and to evaluate a practical methodology to assess the offsite dose of a hypothetical nuclear power plant (NPP) accident at the Ninh Thuan 2 NPP in Vietnam. The dose factor of radioactivity releases in airborne that enter the human body through inhalation exposure pathway is primarily focused to evaluate the human dose of interest. Based on the estimation of offsite dose, this research provides the comparative results of estimating exclusion zone and low population zone by the deterministic and the probabilistic approach. The deterministic approach is the scheme carried out based on the assumption that the weather condition is at steady state along the pathway of radionuclide release. For this approach, the estimation of dose is performed under the unchanged circumstance of a hypothetical worst-case of atmospheric condition. From another perspective, our proposed probabilistic approach takes into account the probabilities of different atmospheric patterns based on our collection of the historical meteorological data in the period from the year of 1996 to 2009. The probabilistic assessment shows the advantage in reflecting the more reality of the NPP accident situation than the deterministic one. The results can be used by the government in planning the critical zones and in producing the evacuation policy in case of NPP accident to limit and minimize the consequence of the radionuclide to the public and the environment.