CMVP1 (cucumber mosaic virus pathotype 1) has been frequently occurring virus causing damage in pepper farms, and it is hard to control the outbreak due to lack of the genetic source resistant to this specific pathotype. Therefore, we have developed transgenic peppers tolerant of CMVP1 using a CP gene of CMVP0 pathogen. In order to fulfill the requirement of the biosafety assessment criteria, we have studied the horizontal gene flow from GM pepper to non-GM pepper by monitoring the transgene movement. If the pepper farms are located closely each other and the pollen moves from GM pepper to non-GM pepper, it would cause unintended fertilization. Therefore, a buffer zone to separate the cultivation regions is required to avoid the contamination of transgene. Previously, several data regarding the movement distance of pepper pollen were reported by judging the phenotypic change. However, no tool as a trace marker was available. The objective of this study was to assess the frequencies of gene flow from GM peppers to non-GM peppers in neighboring farms using the transgene of CP as a trace marker. The GM and non-GM peppers were cultivated in the isolated farm of Nongwoo Bio Co. (NW GM pepper field) and pepper fruits were collected from the NW GM pepper field as well as the neighboring pepper farms. The pepper seeds collected from the farms were planted and the massive PCR analysis was performed to answer the question how far the pollen of GM pepper migrates. The conclusive data based on the consecutive experiments for 6 years is that the gene flow by pollen movement did not occur in peppers that were separated each other over 30 m.