The effect of iron slag powder (ISP) obtained from the local steel industry as an effective addition to improve the radiation shielding ability of cement paste was evaluated. Ten cement pastes with different ISP-to-cement ratios, up to 90 % by mass of cement, were prepared. In addition, the compressive strength of the cement paste as a function of slag content was investigated. The γ-ray attenuation measurements were performed by a NaI (Tl) detector at 59.54, 511, 662, 1,173.2 and 1,332.5 keV. The computation of γ-ray attenuation parameters was obtained by the WinXCom program. Both measured and calculated shielding results are in good agreement. The results demonstrate that the addition of slag significantly alters the cement paste density, γ-ray attenuation coefficient, effective atomic number (Zeff), effective electron density (Neff), and kerma coefficients (k). Moreover, the neutron shielding of cement paste has been evaluated in terms of the macroscopic removal cross section of the fast neutron (ΣR). In conclusion, it is argued that the incorporation of slag results in a significant improvement in γ-ray shielding ability. In addition, the results showed that the best ISP addition proportion that leads to the best shielding properties is about 60 % (by mass of cement).