The purpose of this Paper is to assess and select the preferable and optimum biomass energy source using Analytic Network Process (ANP) for making an efficient Policy in Iran electricity generation industry. There are four major biomass energy sources in Iran comprising agriculture and forest wastes, biodegradable municipal waste, animal manure, and Municipal and industrial wastewater. In this paper, we assess and compare these resources, systematically, based on different Criteria and Sub-criteria derived from literatures and expert’s views to choose the most preferable biomass source for producing required fuel for power plants. The required data will be gathered from experienced experts in Iran Renewable Energy Organization (SUNA). Results show that the criterion “economic and legal factors” has the highest importance (weight) among other identified criteria used in biomass source assessment. In addition, “biodegradable municipal waste” recognized as the most preferable biomass energy source for generating electricity in Iran power plants.