Urban green space plays an important role in providing citizens with recreation opportunities and amenities. It could also contribute to revitalizing neighborhoods when the green space improves the image of disadvantaged communities and attracts people like the case of High Line Park, New York. Environmental gentrification could be defined as the mechanism by which opening of a new park or a green space works as a trigger for gentrification. From a neighborhood small business perspective, urban green spaces could lead to drastic change in retail business: opening of new entrepreneurial retail capital—boutiques, trendy restaurants, and café as well as the replacement of local retail store and services. This study introduces recent policy efforts of Seoul City to make the city greener such as Cheongye Stream Restoration, Seoul-Ro, Gyeongui Line and Gyeongchun Line projects. Then, from the perspective of environmental gentrification, this research explores the outcomes of the urban greening projects using the case of Gyeongui Line Forest Park. Gyeongui Line, which had been underutilized railways, was converted into a linear urban park three miles long and 10 to 60 meters wide. The neighborhoods near Gyeongui Line have been in the process of gentrification, and the opening of Gyeongui Line Forest Park has accelerated and expanded gentrification. In order to explore the environmental gentrification mechanism, this study analyzes the trajectories of retail business before and after the opening of the park. Spatial and temporal characteristics of retail business are analyzed based on the birth and death information of the various small business. The analysis for the trajectories of retail business confirms that displacement of retail services for residences was promoted by the opening of the park. Land use change from residential to commercial use has been increased by the opening of the park. Further, the opening of the Gyeongui Line increased new entrepreneurial retail business. The results and findings of this study provide a better understanding of neighborhood change from the environmental gentrification perspective.