The diffusion coefficient of cupric ion in aqueous CuSO4/H2SO4 solution at 298.1 K is given by D-Cu2+ = {(7.80 +/- 0.25) - (6.34 +/- 1.03)[Cu2+](1/2)} x 10(-10) m(2) s(-1) for 0 to 0.02 mol liter(-1) [Cu2+] in 0.10 mol liter(-1) H2SO4. The value at [Cu2+] = 0 is D(Cu2+)degrees = (7.80 +/- 0.25) x 10(-10) m(2) s(-1), and this value can be used at any H2SO4 concentration ranging from 0 to 0.50 mol liter(-1) without exceeding the error in D(Cu2+)degrees All errors are 95% confidence intervals. These diffusion coefficients were determined with a copper rotating disk after separating the activation and diffusional components of the disk current and after correcting for charge-modified diffusion (migration) and for the approximations used in the integration of mass transport equations in the derivation of the Levich equation. If these corrections are not made, diffusion coefficients containing systematic errors of up to ca. 15% mag be produced. This paper contains some rationalization of the ca. forty literature values for D-Cu2+ which are unacceptably dispersed by +/-80% about their mean. The exchange current density and the transfer coefficient for the Cu2+ --> Cu+ reaction were measured and gave j(o) = 39.2 +/- 2.4 A m(-2) and alpha(c) = 0.28 +/- 0.03, respectively.