Abstract: Huangluugbin is a serere disease of citrus in South China.After we found out that the pathogen was the procaryotic microorganism called rickettsia-like organism or bacteria-like organism in the sieve cells of leaf vein from citrus diseased plant under electron microscope, we also found out the same procaryote in the ultra-thin sections of the salivary gland of psylla (Diapherina citri) which were feeded on the deseaed citrus seedlings and in the sieve cells of the deseased citrus seedlings which were transmitted by the pathogen carrier-psylla.Recently, by using psylla and two kinds of dodders (Cuscuta compestris and c.japonica) as the vector or vector bridge, we studied the transmission of Huanglungbin procaryote from diseased citrus seedling to eight kinds of herbaceous plants. The result show ed that there was only Cuscuta compestris which could transmit procaryote from citrus to periwinkle (Catharanthus roseus).24 out of 25 tested periwinkles showed the typical symptoms, consisting of the first symptom of yellowing vein, then the localized yellowing along the vein and the margin of leaf, and finally the whole leaf yellowing during 3 to 6 month after transmission.Under electron microscope there were numerous bodies of procaryote in the sieve cells from ultra-thin sections of leaf vein of infected periwinkle plant. These pre-caryotes showed spherical, elongate or filamentous shape, 40-600nm, in diameter and 150-1800nm. in length, and with an envelop censisting of a threelayer membrane that was 20-25nm.in thickness.The morphology of procaryote was the same as that of citrus Huanglungbin seedling. In addition, several attempts to transmit procaryote from citrus to periwinkles by Cuscuta japonica and to other seven kinds of herbaceous plants by psylla were unsuccessful.