[ Objective] The aim of this study was to investigate the dynamic distribution of endophytic rhizobia in different plant parts during seed development of alfalfa and the carrying mechanism of endophytic rhizobia from alfalfa seeds. [ Method] Root, stem, leaf, flower, pod and seed from two varieties of alfalfa in different development stages were used for surface disinfection, and then the present site and quantity change of rhizobia in alfalfa were studied by the dilution - plate method. [ Result] The number of rhizobia from underground plants in the same stage was as follows： main root 〈 lateral root 〈 hair root. The number of rhizobia from main root and hair root in different stages was as follows： bearing pod stage 〉 branching stage 〉 florescence, while that from lateral root was as follows： branching stage 〉 florescence 〉 bearing pod stage. The distribution of endophytic rhizobia from aerial plants was as follows： few rhizobia was found in stem during branching stage and bearing pod stage, which accounted for 155 cfu/g and 125 cfu/g respectively. Rhizobia mainly distributed in flower bud during branching stage accounting for 9 400 cfu/g, while only in ovary wall during squaring stage accounting for 18 cfu/5 flowers, and few in pollen （26 cfu/5 flowers）, fertilized ovules （26 cfu/50 grains）, receptacle （15 cfu/5 flowers） and ovary wall （95 cfu/5 flowers） during florescence. Rhizobia existed in pod peel （3 550 cfu/5 pods） and immature seed （1 135 cfu/50 grains） during bearing pod stage, and greatly distributed in seed coat of mature seeds （1 435 cfu/50 grains）, but only few in embryo （32 cfu/50 grains） and cotyledon （22 cfu/50 grains）. [ Cenclusion] There is a significant difference in the distribution of endophytic rhizobia from different parts of aerial alfalfa, which only exists in the parts directly related to seed development.
