The term Underused Urban Spaces (UUS) refers to spaces within urban areas that have become unused, or that are being used to a lesser degree than they could or should be such as former industrial zones, abandoned facilities or buildings and Expo or Olympic Games cities. The Islamic pilgrimage sites known as Hajj sites (HS) are considered form of the UUS concept as they are used lesser degree than they should be. However, the emergence of such spaces has therefore encouraged researchers, urban planner, social and local authorities to discuses about the appropriate decision regarding their future towards conversion or alternatively using those spaces in order to achieve positive social, economic and environmental benefits, according to Pagano and Bowman (2000), UUS can be a powerful tool for governments and investors to use during the urban growth (UG) of their cities. Since, remote sensing and GIS technologies are used recently to study and analyze the UG of cities; the main objective of this paper is to demonstrate the efficiency of those technologies in addressing the future decisions regarding the underused status of Hajj sites in relation to UG of the city of Mecca. Tow classified land cover maps of Mecca for two years (1998 and 2013), in addition to entropy index and multiple regression analyses were utilized in order to quantify the relationship between HS and Mecca UG. The results showed that the urban growth of Mecca has increased by approximately 56%, and almost 32% of that increased were around HS in on hand, and on the other hand the entropy and the regression analysis showed that there is 51% probability that the future growth to be also around HS. These findings will better addressing the future decisions regarding the underused status of HS, simultaneously revel that the use of RS and GIS was highly effective to be adopted within similar cases of UUS.