Abstract:Yellows disease of betel nut palm Areca cathecu was observed in a commercially operated herbal farm in Danzhou County,Hainan Province in 1981.Since then this disease has affected over 90% of betel nut palms in this farm and is found in other betel nut growing areas in the island. Symptoms of the infected palms include the overall leaf yellowing,water soaking marks on leaflets, reduced spear leaf size, proliferation of auxiliary buds, recrosis of inflorescence and premature nut falls. The death of infected palms occurred one year after symptom expression. Electron microscopic examinations revealed that bacteria-like organism (BLO) was found in thin sections of vascular bundles and parenchyma cells of the infected tissue. The BLOs were measured at 460-780nm×360-570nm with 30-40nm thickness of cell walls. In addition, the mycoplasma-like organism (MLO)was found in sieve cells of phloem tissue.The sizes of MLOs ranged from 380 to 560nm . The thickness of unit membrane was measured at 10nm . No BLOs and/or MLOs were found in thin sections of healthy tissue.