Resources’ scarcity, especially in developing countries, has caused allocation essentially among competing activities to create value. The importance of resource allocation would be more understood if we pay attention to growing complexity in societies and economic development problems they face. In the context of the national economic development literature, the notion of “Key or Critical Sectors” has become an accepted component of development strategy. By and large, key sector analysis is an attempt to determine the economic effect of a sector in a given economy. From macroeconomic point of view, Agriculture and Non Agricultural Manufacturing (NA-Manufacturing) as two parts of production sector, compete for absorbing limited resources. This paper with using 31 indices; factor analysis; numerical taxonomic analysis; and three level of assessment aims to answer the question of which one of these two is the key sector, and be a completion to previous studies which their common deficiency is the lack of indices. Results of this study for Iran economy show that Agriculture sector is preferred to NA-Manufacturing sector.