This article problematizes relation between urban expansion and socioeconomic vulnerability, with reference in Caicó city (Brazil) and from 1980s to current days as temporal cut. Urban expansion of Caicó was analyzed by occurrence phases, taking into consideration population, economy and city specialty variables, calculating socioeconomic vulnerability indexes and levels by geographic zones and neighborhoods of that city, from which a cartography related to this thematic was produced. Methodologically, a document e bibliographic research was conducted. Thus, cartography of socioeconomic vulnerability in Caicó, by geographic zones and neighborhoods, reveals that indexes and levels related to this phenomenon do not present great variations, situating between medium and very low; however, West Zone presents highest socioeconomic vulnerability, being João Paulo II neighborhood one that holds city’s highest index. Furthermore, It was found that although average Índice de Vulnerabilidade Socioeconômica por Bairros (IVSB) has been registered on ancient formation neighborhoods, its occurrence is stronger in recent formation neighborhoods. In this sense, It is possible to infer that socioeconomic vulnerability in Caicó city is associated to urban expansion process, once this phenomenon becomes more present in recent formation neighborhoods, generally situated in peripheries of cities, where lower purchasing power populations are located, and public politics are more neglected.