The relativistic effects on absolute magnetic shielding tensors (sigma(Se)) are explicitly evaluated for various selenium species (40 species) with the DFT(BLYP)-GIAO method. Calculations are performed under relativistic and 200 nonrelativistic conditions with the Slater-type basis sets in ADF 2010 in the framework of ZORA, employing the optimized structures under nonrelativistic conditions at B3LYP of Gaussian 03. Quadruple zeta all electron with four polarization functions (QZ4Pae) are mainly applied to evaluate sigma(Se). Ranges of the effect on diamagnetic (ad(Se)), paramagnetic shielding tensors (sigma P(Se)), and sigma(d+P)(Se) (=sigma(d)(Se) + sigma(P)(Se)) are -24 to -20 ppm, -115 to -3 ppm, and -136 to 26 ppm, respectively. The spin orbit terms (sigma(so)(Se)) are evaluated to be 92-225 ppm with QZ4Pae, which clarifies the effect on total shielding tensors (rho(t)(Se) = sigma(dtP) (Se) + sigma(s)(Se)) to be -8 to 152 ppm, at the spin-orbit ZORA level. The calculated at(Se) values reproduced well the observed values.