The radiation-induced bystander effect is defined by the presence of biological effects in cells that were not themselves in the field of irradiation. Plasma, as the fourth state of matter contains numerous active components including photons, free radicals, mild heat, electrons and ions. Cold atmospheric plasma (CAP) has been widely applied in biology and medicine including cancer treatments. However, contributions of CAP induced bystander effect have not been studied. Proteomic profiles obtained from direct CAP-exposed and un-irradiated (bystander) A549 cells were compared to understand enriched proteins or pathways altered under the bystander conditions.