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The magnitude of economic growth depends on the growth and investment in key economic sectors. Thus, one important goal of policy makers and economic planners in any society is to identify key economic sectors. This paper aims at identifying these sectors in Iranian economy using stochastic input-output analysis. Stochastic analysis is used to investigate how the inherent imprecision affects the concomitant key sector analysis in case of utilizing aggregated data. The analysis is based on Iranian input-output table for the year 2001, using distance estimation and Monte Carlo simulation. Results of the non-stochastic approach indicate that among 25 economic sectors in aggregated input-output table, six sector-groups are the key sectors while, in non-aggregated input-output table with 99 sectors, 13 sector-groups can be identified as key sectors. Finally the suggestion is that to identify key economic sectors the non-aggregated input-output table should be used.