Abstract: Building on previous studies of one- and two-dimensional reduced element, the applicability of the reduced element methodology to three-dimensional finite element analysis is investigated. Several key issues, including element selection, shape-function formulation, mesh subdivision, and hanging-node treatment, are explored. The hexahedral three-dimensional reduced element based on hierarchical shape functions is developed, and adaptive analyses are performed. The three-dimensional Poisson equation and elasticity problem are employed to evaluate the proposed approach. The accuracy of the error estimation and the effectiveness of local mesh refinement are examined through numerical examples. The results show that the proposed method yields reasonable error indicators and automatically generates adaptive meshes according to local solution features. The prescribed error tolerance in the maximum norm is achieved through adaptive refinement, demonstrating the feasibility of extending the reduced element methodology to three-dimensional finite element analysis.