The purpose of this study is to analyze the impact of tactical urbanism applied in Seoul on the formative factors of placeness and change in perception of placeness. To this end, a survey of visitors to ten locations that have used tactical urbanism in Seoul has been conducted, and the results were analyzed. The findings of research are as follows: First, the better the characteristics of tactical urbanism were perceived, the better the formative factors of placeness of a target area were also recognized. Second, the characteristics of tactical urbanism did not directly affect change in perception of placeness. Third, the formative factors of placeness of a location using tactical urbanism had a significant effect on change in perception of placeness. Fourth, when the characteristics of tactical urbanism affect change in perception of placeness, the formative factors of placeness play a mediating role.