Potato viruses X and Y were used for study the effect of the two viruses on the metabolism of potato plants. It was found that detectable decrease or dry matter, total nitrogen, tuber Starch, number of starch granules, and total protein. The nucleic acid content of infected plants increased than healthy ones. The investigated hydrolytic enzymes of amylase and protease were reduced in infected potato plants while the level of polyphenol oxidase and peroxidase was increased. PVX and PVY infected potato plants contained less auxins and gibberellins, and the pattern of growth promotors and growth inhibitors was altered. Cytokinin was also inhibited as a result of virus infection. Examination of epidermal strips of infected potato plants revealed the presence of cytoplasmic inclusions. Many cytopathic effects showed in potato leaves such as presence cytoplasmic vesicles, abnormal appearance of grana and change of mitochondria.