As a vast country with average solar radiation of 4.5 kW-hours per square meter, Iran enjoys a very high potentiality for initiating and utilizing solar systems and, in particular, electricity generation from solar power plants. Optimal site selection for solar power plants requires making multi-criteria decisions. Analytic Hierarchy Process (AHP) is one of the most comprehensive multi-criteria decision-making tools. The present study was conducted to select a regionally optimal site regarding climatic conditions using AHP and the Expert Choice software. Certain criteria and sub-criteria such as the amount of radiation, the number of sunny days, the average temperature, the amount of humidity, the amount of rainfall, the level of visibility, and the cloudiness factor were regarded. To select an optimal site using AHP and Expert Choice software, after specifying the hierarchic levels, including the target, criteria, sub-criteria, and alternatives (intended sites), pairwise comparison was made between the sets to weigh them up. The provincial centers of Iran were considered in the study and Zahedan has been selected as the best location for constructing a solar power plant. Moreover, a sensitivity analysis on the major criteria was performed and the impacts of parameter weight on the alternatives were assessed.