Cucumber mosaic virus (CMV) is one of the most devastating viral pathogens that cause severe problems for several plants in Egypt and worldwide. In the current study, the electron microscopic observation of spherical with a diameter between 27.49 to 30.53 nm and the yield of the purified virus was 1.4 mg/100 g infected leaves. Results of the mechanical inoculation revealed severe mosaic and chlorotic symptoms and were observed on Cucurbita pepo after ten days, while no signs appeared on the mock-inoculated plant. The ultra-thin sections of CMV-infected C. pepo leave judged by I-ELISA revealed the presentence of CMV-like particles using transmission electron microscopy. In addition, accumulation of starch grain was observed as cytopathological effects of C. pepo leaf affected by CMV-infection. Moreover, the formation of double-membrane bodies in the parenchyma and chloroplast malformation was also reported.