As quoted in the report by Census & Statistics Department in July 2015, “there were 85,500 households representing 195,500 residents living in sub-divided units (SDUs) in Hong Kong and those units are mainly located in old residential buildings”. The emerge of this kind of housing is mainly due to the continuous high rent and an increasing number of low-income people and families whose income level are just higher than the income limit for applying the Public Rental Housing (PRH), but at the same time, they are not able to pay for the high rents for private domestic flats. The landlords and owners took advantage of this special phenomenon in Hong Kong and sub-divided their flats into two or more individual units for renting. With its specific physical, social and legal characteristics, those SDUs have become an informal living solutions and it represents various invisible social layers and social classes in an affluent society like Hong Kong. This paper will focus mainly on the causes, current situation and prospect of the subdivided housing units in Hong Kong’s old districts like Shamshuipo and Wan Chai. Survey questionnaire and interviews will be conducted with the tenants living in SDUs and with a voluntary organization, the Society for Community Organization (SoCO) that provides assistance to the residents living in SDUs. Besides that, the Long Term Housing Strategy (LTHS) will also be studied in order to review whether it could solve the housing problems of the families living in this kind of housing units. To collect data and evidence, survey would be conducted and a structured questionnaire containing the following analytical framework and research questions will be used: a) To review the root causes and the development of increasing trend of SDUs from owners’ and residents’ perspectives; b) To explore the psychological effect such as the self-image and personal interactions for the residents living in the SDUs; c) To study the social implications such as the neighborhood relationship and social network for the people living there; and To analyze the position of government policy in housing supply and the measures proposed by the government, such as the licensing scheme or the landlord registration system, in tackling the problem of SDUs Other than the data collected from the survey questionnaire and interview conducted, some other data such as government and NGOs’ reports, news and statistics will also be used to supplement the inadequacies of the data. With all the findings and data analysis, a clearer picture and conclusions will be drawn on the SDU phenomenon and its social implications in Hong Kong Finally, recommendation and suggestion will be made based on the data collected from the questionnaire and the valuable comments from the interviewees. It hopes that this research would arouse the attention from different stakeholders and policy makers, so as to improve the situation of sub-divided housing problem in an affluent city like Hong Kong. ; published_or_final_version ; Housing Management ; Master ; Master of Housing Management