Professionals play a major role in determining the success and failure of constructionrnprojects, since they have direct involvements in every stage of the construction. Taking thatrninto consideration, this research is conducted to identify the practice of professional ethicsrnand its effect on 20/80 condominium projects. It also uncovered the most prevalent unethicalrnpractices in 20/80 condominium projects and the contributing factors for those unethicalrnpractices. A questionnaire survey using random sampling and interviews using purposivernsampling were conducted on professionals currently working on 20/80 condominiumrnprojects. rnThe findings indicate that various forms of unethical conducts are prevalent in 20/80rncondominium projects which are adversely affecting the quality, time and cost of thernprojects. The most unethical practices on the side of the contractors were found to be theft;rnillegal bidding practices, purchasing substandard materials to save money, negligence andrnlack of qualification. Whereas, consultant related unethical practices were found to bernnegligence, bribery, lack of loyalty to the client and compromising quality for oneâ€Ÿs ownrnpersonal need. Fraud in the BOQ, high cost estimation to share excess cost, negligence andrntaking biased measure are the most unethical practices of the quantity surveyors.rnThis paper also suggests ways to enhance ethical professionalism among constructionrnprofessionals including: imposing heavier penalties on those who are found to actrnunethically, giving ethics-training programmes, creating a strong management team andrnstrict monitoring and evaluation in every stage of the project. rnProfessional ethics is a pre-requisite to attain a sustained and acceptable standard of successrnin 20/80 condominium projects, due to that serious attention has to be given to complete thernprojects with the planned time, planned budget and the expected quality. The findings fromrnthe study are expected to give a good base to the government, construction professionals andrnthe policy makers in detecting and preventing unethical practices in 20/80 condominiumrnprojects of Addis Ababa.