organic acids: α-ketoglutaric acid, fumaric acid and succinic acid. 3. As to the relation between the C/N ratio (sucrose/Na-glutamate) of the medium and growth of X. oryzae, much vigorous growth was obtained in the case of culture with the concentration of 1.5 per cent sucrose and 1.0 per cent Na-glutamate as the carbon and nitrogen source. 4. From the above results obtained, a new synthetic medium for X. oryzae is accomplished by modification of Starr's syntetic medium. The composition of a new synthetic medium is as follows : sucrose 1.5 g, Na-glutamte 1.0 g, KH_2PO_4 0.2 g, MgSO_4·7H_2O 0.02 g, B(H_3BO_3) 0.5 μg, Ca(CaCO_3) 10.0 μg, Cu(CuSO_4·5H_2O) 1.0 μg, Fe(FeSO_4(NH_4)_2SO_4·6H_2O) 10.0-50.0 μg, I(KI) 0.1 μg, Mn (MnSO_4·H_2O)1.0-2.0 μg, Mo(MoO_3)1.0 μg, Zn (ZnSO_4·7H_2O) 5.0 μg and 100 ml of distilled water, PH 6.8. This modified synthetic medium is suitable for estimation of the bacterial growth by means of photometric apparatus because it causes no precipitation in medium by heat treatment.