In the cities of developing countries especially in sub-Saharan Africa, poverty, unemploymentrnrate, poor living condition, lack transparency and accountability, lack of good governance arernthe major factors to contribute for the people to hold land informally and built houses forrnresidential or other purposes. In most of Ethiopian cities informal settlement is highly seen inrnperipheral areas this is because people can easily to hold land for housing from local farmers,rnbrokers, speculators without permission from concerning bodies. Thus, studying the contributingrnfactors for expansion of informal settlement was found to be a crucial.rnThe general aim of the study is identify factors that contribute for expansion of informalrnsettlement and examine its impact on urban land Administration in Yeka sub city, Addis Ababa,rnEthiopia.rnA combination of both quantitative and qualitative methods can complement each other andrnallow for more complete analysis my study. Accordingly, in this study a mixed approach methodsrnwhich is a procedure for collecting and analyzing both quantitative and qualitative data havernbeen used. However, during the study peripheries of woreda of the sub city that means woredarn10, 12 and 13 were selected with regard to with reliability and validity thoughts. From this totalrnthree woredas eleven ketenas has been identified for the study.rnIn periphery area of Yeka sub city, particularly woreda 10, 12, and 13 illegal houses buildingrnwas expanded from time to time. Farm plot were the highest vulnerable plot for the expansion ofrninformal settlement in this study area (that means about 55% of the illegal built houses) werernexist on the area which was far previous.rnOn another hand, day to day the population which was migrated from rural to urban area to gotrnjob opportunity has been highly settled in this periphery area temporarily, thus, to use thisrnopportunity as revenue generation, illegal house construction was held.rnIn periphery area to ensure the development of urban land and protect it from being informalrnsettlement, actively involvement of all stockholder will be very important starting from planningrnto implementation