The present invention relates to Rhizobium sp. KB10 strain having properties of promoting growth of Botryococcus braunii, which is an alga capable of producing biodiesel, and also enhancing production performance of biodiesel. Mores specifically, it relates to novel Rhizobium sp. KB10 strain which has properties of promoting growth of Botryococcus braunii used for biodiesel production and also enhancing content of C18 (i.e., oleate) corresponding to high quality biodiesel component as much as 900%. By using root colonizing bacteria like Rhizobium, it is possible to promote effectively the slow cell growth of Botryococcus braunii and increase as much as possible the oleate amount, which is a high quality biodiesel component. Further, by carrying out mixture culture using such bacteria, problems associated with contamination by other microorganisms during a process of producing biodiesel by culture in an outside environment can be dramatically solved.