This study aims a comparative analysis of social stratification in the Great Seoul area using two types of population. One type of population is a resident population(常住人口), and the other is a daytime population주간인구(晝間人口). In most demographic studies, only resident population have been considered. There has been less attention to daytime population. However, a resident population have a character of night population야간인구(夜間人口). In fact, most people move and work in the areas where they do not live in everyday life in the contemporary period, which indicates that the concept of a daytime population is more significant than that of a resident population. This study reveals that a number of people, on the one hand. come together to the downtown area to work or study while they live in other areas. On the other hand, resident population in downtown area do not move so much. When we analyze the social stratification structure of the Great Seoul area using a resident population, we find that the resident population of downtown area consist of those of low social status. On the contrary, the daytime population of downtown area in Seoul consist of those of high social status. This means that most people of high social status live in the southern area of Seoul or outside Seoul, but make a living in downtown area in everyday life. From this study, we find that the concept of a daytime population is as important as that of a resident population. The more residence becomes separate from work place, the more the significance of the concept of a daytime population grows in making policy as wall as in demographic studies. This study implies that we need to pay more attention to the concept of daytime population in demographic and sociological Studies.