This study aims to identify the income instability of Seoul citizens and to seek alternative income security systems which effectively decrease the income stability of Seoul citizens. Although various income security systems are being implemented to respond to the loss of income of the people, they are insufficient to respond to the risk of income insecurity amongst citizens. Efforts have been made to improve the system, such as, upgrading the system to identify households in crisis, such as, blind spots in welfare. However, the tragic situation of not being protected by the social safety net and ending their own lives is recurrent. This shows that the existing income security system is not responding to income instability. Therefore, it is necessary to identify the pattern of income instability that Seoul citizens face and to empirically examine what alternative systems are effective in alleviating the income instability of Seoul citizens. In this study, based on data from the Korea Welfare Panel Survey, the status of income instability amongst Seoul citizens was analysed in terms of longitudinal income mobility and poverty dynamics. Moreover, using simulation analysis, we empirically analysed which model effectively alleviated income instability amongst the negative income tax (NIT) and basic income (BI) categories.