We propose a method for constructing

�rational splines in

�over a���triangulation, via a finite element approach, which generalized for tetrahedrons, the construction proposed in [1] for triangles. For

�the usual polynomial splines require some super-smoothness at the vertices of the tetrahedron, even when dealing with macro-elements. This is no more��a requirement for our rational approach. This method can also be generalized to simplices in �

: rational finite element, trivariate spline, finite element.