In this paper, hierarchical mass-assignment fuzzy systems of two types are presented, based on mass assignment theory. It is constructively provedt hat hierarchical mass-assignment fuzzy systems of these two types are also unive rsal approximators. Because of the fact that the number of rules in type 1 hiera rchical mass-assignment fuzzy systems increases linearly with the number of input variables and that fuzzy systems are added up to type 2 hierarchical mass-assignment fuzzy systems in terms of different accuracy requirements. These two types of systems can be effectively used to overcome rule-explosion problem, that is , the number of rules increases exponentially with the number of input variables.