Phytopathogens have evolved diverse independent and complex modes of penetrating and accessing plant cellular contents. The synthesis of reactive oxygen or nitrogen species (ROS/RNS) by the utilization of molecular oxygen during plant–pathogen interactions results in to oxidative burst, a signaling cascade to defense. ROS array includes singlet oxygen, the hydroxyperoxyl radical, the superoxide anion, hydrogen peroxide, the hydroxyl radical and the closely related reactive nitrogen species, nitric oxide. ROS acts synergistically directs to signal amplification to drive the hypersensitive reaction (HR) and initiates systemicdefenses. The role of ROS in successful pathogenesis, it is ideal to inhibit the cell death machinery selectively and simultaneously to monitor other defense and pathogenesis-related processes. With the understanding of the interplay underlying the localized activation of the oxidative burst following perception of pathogen avirulence signals and key downstream responses including gene activation, cell death, and long-distance signaling, novel strategies will be developed for engineering enhanced protection against pathogens by manipulation of the oxidative burst and oxidant-mediated signal pathways. In this over review, it is reported the different roles of ROS/RNS in host–pathogen interactions with example on Alternaria- Sesamum interaction.