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Rhizobial inoculants play much important role in increasing the efficacy of symbiotic N2 fixation in leguminous plants. This research was conducted toward preparation of Rhizobium inoculant for beans (Phaseolus vulgaris L.) and formulation of carrier using native inorganic and organic substances. In this study efficacy of 15 compounds, including simple basic compounds and their combinations, were evaluated with reference to their capacity for maintaining high concentration of active bacterial population. Physical characteristics including moisture, water-holding capacity, pH, ash and fiber content designated and the combinations were prepared by mixing of these compounds. A collection of nitrogen fixing Rhizobia was isolated from roots of native varieties of the mentioned plants and preserved as pure cultures under appropriate condition. Foregin strains were obtained from CIAT. Each of the compounds was packed in polytene bags and gamma sterilized. Sufficient amounts of bacterial suspension were added to the carrier compounds to prepare the inoculants containing uniformly distributed bacteria. Getting samples from each of the inoculants and determining viable cell count over a 137 d period revealed the performance of inoculants made from coal-containing mineral soil. Nodulation tests were carried out according to two different procedures: 1) under sterile condition (in vitro) and 2) in non-sterile condition (in vivo). Nitrogen fixing ability was qualified by quantifying of nodule formation and also by measuring of acetylene reduction capacity in nodules. The superior N2 fixing quality was determined in strains 1 and 7001. Results showed that mixed complex compounds generally acts better than simple compounds in maintaining higher levels of active bacterial population and bacteria could survive in concentrations as high as 109 CFU g-1 over a four months period. Two types of carriers including J (a mixture of coal containing mineral soil, peat-like compound and prelate) under sterile condition (in vitro), and A (containing peat like compound) under unsterile condition (in vivo) showed the best results and maintained active Rhizobia at high concentrations 109 and 108 CFU g-1, respectively. In comparison, after a 4 month period concentration of bacteria in peat like carrier was 107 times more than that of weak carriers such as D (bagasse containing carrier).