The surface magnetic field configuration of the Ap star 78 Vir is reconstructed in the framework of the magnetic charge description (MOD) method from the analysis of Stokes I, Q, U, V spectra obtained using the MuSi- CoS spectro-polarimeter at Pic-du-Midi Observatory. Six magnetically-sensitive Cr u lines are analyzed using polarized spectrum synthesis, supposing a nonuniform chromium distribution over the surface of 78 Vir. We show that the global magnetic field structure of the star can be well described by a slightly decentered magnetic dipole model, which provides the best fit to the majority of lines analyzed at the level of x2 = 2.77 ÷ 6.84. Derived inclinations of the stellar rotational axis to the line-of-sight, i = 26°, and to the magnetic dipole axis, 13 = 125°, as well as the sky-projected position angle of the stellar rotation axis, 115°, agree reasonably well with the results of an Fe II line analysis, and with previous estimations by other authors.
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