An isolate of cucumber mosaic virus (CMV) was obtained from naturally infected guava (Psidium guajava L. cv. Balady) plants grown in Minia Governorate, exhibiting systemic green island and characteristic mosaic symptoms associated with deformation pattern. The isolated virus infected thirty-two plant species, using different varieties and cultivars. The virus reacted systemically with mosaic alone on 9 test plants out of 32, while some other in combination with other showed symptoms, i.e. crinkling, vein clearing, vein banding, deformation, stunting, wilting, deformation, necrosis, yellowing and
green island. The virus under investigation was inactivated in sap after heating for 10 min at 70oC.The dilution end- point was between 10-4 and 10-5 .Virus infectivity in vitro was maintained more than 10 days storage at room temperature (25oC). The identification of the virus under study was confirmed serologically by DAS-ELISA. Positive reaction obtained indicated that the tested virus was related serologically to Cucumovirus. Light microscope examinations revealed amorphous cytoplasm inclusions (X-bodies) in the epidermal-hairs cells of squash (after 21 to 42 days from inoculation) with the tested virus. Electron micrographs observations of ultrathin sections in the infected cell with the isolated virus were: some abnormalities in the cell wall, degradation and malformation and showed conspicuous alterations in shape, malformed mitochondria, swollen of chloroplast, virus particles were found in the cytoplasm, around and in the chloroplast, 3-par mural bodies were also seen in the chloroplast.