Self-diffusion coefficients D of the trivalent ions in aqueous solutions of Eu and Gd have been determined in electrolyte support Gd(NO 3 ) 3 , and of Am, Bk, Cf and Es in electrolyte support Nd(ClO 4 ) 3 , in concentrated solutions at (pH = 2.5) HNO 3 , HClO 4 and at 25 Β°C using the open end capillary method (O.E.C.M.). This method measures the transportation time of ions across a fixed distance. In this paper we complete a measurement of self-diffusion coefficient at concentrated solution (1.5 M). We optimized the pH in order to avoid the hydrolysis, pairing and complexing trivalent 4f and 5f ions. The behavior of D and DΞ· are plotted versus βC. The similarities observed of self-diffusion coefficients of trivalent f-elements ions can be explained by a similar electronic configuration and same hydration number. The variation of D versus the square root of the concentration of the solution was found to be quasi-linear in the studied concentration range (C β€ 1.5 M). Results of the diffusion for the two couples (Am-Eu) and (Bk-Gd) show us that 4f and 5f elements, having similar electronic configuration and/or sub shell half-filled configuration of trivalent ions, have the same behavior. We compared variation of D/DΒ°versus βC for all studied 4f and 5f elements from concentration 0 to 1.5 M and we obtained the same variation with βC for all studied elements. We have estimated activity coefficients for both 4f and 5f trivalent ion elements using Nernst-Hartley expression. We deduced that we can achieve self-diffusion experience using 4f support electrolyte as Nd(ClO 4 ) 3 in acid medium and needing only some 5f element tracer element. This method is adequate for the study of 5f element which is not available as a macro element such as heavy 5f elements fermium Fm 3+ and mendelevium Md 3+ .