In the late 19th and early 20th century,beside allfast changes in western societies,architects alsostarted to abandon past styles toward a form ofarchitecture that had regarded to functional concernsand had no roots in classic styles.After World WarI,this new tendency in architecture(ModernArchitecture)were developed simple,geometric figuresand unadorned facades which deserted any use ofhistorical references.After extension of the Iraniancommunication with western countries,tendenciestoward Modern Architecture extended in Iran.As aresult,since beginning of 20th century,beside gradualpolitical,economical,cultural transformations inIranian society,some of the dominant characteristicsof Iranian architecture began to be changed.Thispoint was an inception for new architecturaltrends,in Iran. One important Iranian habitats thatwere affected roughly, were residentialbuildings.This study was intended to determine theeffects of Modern Residential Buildings characteristics in respect to formal design issueslike free plan,free façade...as well as functionalissues like Separation of bedrooms for family membersregarding to contemporary residential buildings inTehran.