Abstract: Based on the successful transmission and back transmission, Viuca rosea was proved to be a host plant of the yellow shoot BLO. The typical symptom on both sweet orange and Vinca rosea seedlings was shoot yellowings The BLO was found to exist in the phloem cells of the diseased plant of Vinca rosea and sweet orange including the aweei orange plant from which the BLO iras transmitted and to which the BLO was back transmitted!. The BLO was measured to be 360-600 nm in length, 100-120 nm in width, with a unit membrane (or cell wall) of 25-30 in thickness.