Potato virus X (PVX) causes severe losses in worldwide crops of family Solanaceae. Dramatic biochemical changes in virus infected plants due to decrease in qualitative and quantitative of yield crops. The current study demonstrate the changes of biochemical responses as a defense level and resistance genes in infected plants against virus infection. PVX isolate was confirmed by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) . This study was performed on five cultivars of imported seeds potato PVX tested, Diamond , Hermes , Lady Rosetta , Nicola , and Spunta . All potato cultivars were infected with PVX isolate. The five potato cultivars showed variations symptoms development, disease severity and virus concentration .The potato cultivars against PVX infection exhibited significantly  increase  in physiological alterations (electrolyte leakage, cell membrane stability and transpiration rate) and biochemical responses defense (total proline, stabilizing phenols, scavenging enzymes, catalase, peroxidase, polyphenol oxidase, superoxide dismutase, activities) and  RX1 ,  RX2 ,  RX3 genes resistance compared to healthy ones. According to viral assessment, physiological parameters, biochemical responses and RX resistance genes   , the five potato cultivars were divided to resistant cv., Diamond, tolerant cv., Hermes, Lady Rosetta, Nicola and susceptible cv., Spunta