Radiation-induced bystander effects refer to the induction of biological effects in cells that are not directly traversed by an ionizing radiation. The bystander effects might lead to cell death, chromosome aberration and gene mutation. Therefore it is pertinent to study the prevention of these bystander damages. Reactive oxygen species (ROS) were suggested to be involved in bystander effects. In this study, epigallocatechin gallate (EGCG), which is the most active antioxidant component of catechins, were used to scavenge ROS in different systems. In order to allow alpha particles to reach the living cells, thin Mylar films and polyallyldiglycol carbonate (PADC) films were used as cell-culture substrates. The objective of this study is to investigate the scavenging effect of EGCG in radiation induced bystander effect. Different biological methods such as mirconucleus (MN) formation, ionizing radiation-induced foci (IRIF) formation of p53 binding protein 1 (53BP1) and terminal dUTP transferase-mediated nick end-labeling (TUNEL) assay would be used to study the effect. In the first part of this study, Mylar-film based cell-culture Petri dishes were used in the medium transfer experiments to detect bystander effects induced in Chinese Hamster Ovary (CHO) cells by 0.3 cGy/s alpha-particle irradiation. The bystander responses were measured as MN formation. Different concentrations of EGCG were added before irradiation. The results indicated that EGCG scavenged ROS at a significant level in the bystander cells, which was found to decrease in the percentage of MN formation. Moreover, it was found that the signaling molecules secreted by irradiated cells at early time after irradiation was crucial to the initiation of bystander responses. In the second part, the Mylar-film based cell-culture Petri dishes were used to coculture irradiated and bystander cells. 53BP1 forms foci at DNA double-strand break sites and is an important sensor of DNA damages. Our results showed that 53BP1 foci were elicited in bystander cells immediately after alpha-particle irradiation. It was also found EGCG prevented the formation of 53BP1 foci in bystander cells The relationship between the radiation dose and induction of DNA damages in bystander cells was investigated in the last part of this study. Custom-made Petri dishes with thin PADC films were used to quantify the number of alpha-particle hits on the cell nuclei. The DNA strand breaks in the bystander cells induced by 5 MeV alpha particles were quantified with the use of TUNEL assay. The results showed that bystander damages occurred at very low doses and they did not increase significantly with dose. In addition, fewer DNA strand breaks in the bystander cells were observed by adding EGCG before irradiation.