© 2022, The Author(s) under exclusive licence to Australian Ceramic Society.Radiation is now used extensively for a variety of industrial, agricultural, and radiation therapy objectives, as well as other uses, thanks to the advancement of technology. Due to the destructive effects of radiation, radiation protection is so necessary. Although lead and lead-based composites are conventional materials for radiation shielding, their toxic nature restricted the use of them as proper shields. Therefore, the shielding properties of a series of lead-free relaxor ceramics, namely (1 − x)K0.5Na0.5NbO3–xLa(Mn0.5Ni0.5)O3 ceramics are investigated in this study. In order to obtain the neutron and gamma-ray shielding characteristics, the linear attenuation coefficient (LAC, cm−1) and related parameters for (1 − x)K0.5Na0.5NbO3–xLa(Mn0.5Ni0.5)O3 (where x = 0.01, 0.05, 0.07, 0.10, 0.15, and 0.20) ceramic are estimated (abbreviated as (1 − x)KNN–xLMN)). Using FLUKA simulating code and Phy-X:PSD software, the shielding performance of neutrons and gamma rays is evaluated for wide energy ranges. Findings show that the S6 sample possesses the lowest mean free path (MFP) and half value layer (HVL), while the S1 sample owns the highest MFP and HVL. At an energy range between 0.001 and 0.1 MeV, sudden jumps are observed for Zeff and Neff graphs, which may be due to the K-edge absorption of elements such as K, Na, Nb, La, Mn, and Ni. Moreover, the fast neutron removal cross-section (FNRCS) varies between 0.060 and 0.106 cm−1 from the S1 to S6 samples.