The hexadecapole deformation parameter beta(4) Of the rare-earth and actinide nuclei is investigated in the framework of the sdg interacing boson model. An explicit relation between the geometric hexadecapole deformation parameter beta(4) and the intrinsic deformation parameters epsilon(4), epsilon(2) are obtained. The deformation parameters beta(4) of the rare-earths and actinides are determined without any free parameter. The calculated results agree with experimental data well. It also shows that the SU(5) limit of the sdg interacting bosom model can describe the beta(4) systematics as well as the SU(3) limit.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000073668200007&De...