Globally, preeclampsia and gestational diabetes mellitus are known to have an average prevalence ofrn6% and 4% respectively. Both clinical conditions are thought to impact on morphophysiology ofrnplacenta. Placenta is a dual sourceorgan that structurally and functionally connects the developingrnfetusrntornthernuterinernwallrnduringrnpregnancy.rnThisrnfetomaternalrnorganallowsuptakernofrnnutrients,elimination of wastes and exchange of gases. Pregnancy is usually complicated byrnpreeclampsia and gestational diabetes mellitus, which in turn will alter the macroarchitecture andrnfunctions of the placenta as well as health of the pregnant mothers. Hence, this study was conducted tornassess the macroarchitectural changes of placenta in preeclampsia and gestational diabetes mellitusrnmothers as compared to uncomplicated mothers who gave birth at Gandhi Memorial and Black LionrnSpecialized Hospitals, Addis Ababa, Ethiopia. It was an observational comparative cross-sectionalrnstudycarried outat Gandhi and Black Lion Hospitals, from June, 2016- August, 2016. A total of 125rnfresh placentas from uncomplicated, preeclampsia and gestational diabetes mellitus mothers werernimplemented. Themacroarchitecture of placenta were examined by inspection and measuring. The datarnwere analyzed by independent- samples t-test and chi square. Accordingly, the finding shows that thernshapes of placentas were circular in 80% of uncomplicated, 72% of preeclamptic and 76% ofrngestational diabetes mellitus, while oval in 14% of uncomplicated, 20% of preeclamptic and 8% ofrngestational diabetes mellitus. In addition, it was irregular in 6% of uncomplicated, 8% of preeclampticrnand 16 % of gestational diabetes mellitus. The weight of placenta in uncomplicated, preeclamptic andrngestational diabetes mellitus mothers respectively were 499.4, 456.20 and 583.68 gram. The numbersrnof cotyledon were 18.66 in uncomplicated, 17.24 in preeclamptic and 22.56 in gestational diabetesrnmellitus mothers. The diameter was19.4, 17.66 and 23.50 centimeter in order of uncomplicated,rnpreeclamptic andgestational diabetes mellitus mothers. The thicknesses were1.96centimeterrninuncomplicated, 1.72centimeterin preeclamptic and 2.34 centimeterin gestational diabetes mellitusrnmothers. According to the present study most of macroarchitecture (diameter, thickness, weight andrnnumber of cotyledon) of placenta were significantly decreased in preeclamptic and increased inrngestational diabetes mellitus mothers