Abstract: Biochar and biochar composites are versatile materials that can be used in many applications. In this study, biochar was prepared from sawdust and combined with the yttrium iron garnet (YIG) nanocrystal to investigate the shielding effectiveness of the composite structure. Firstly, the effect of the pyrolysis temperature on the shielding effectiveness of biochar was investigated. Secondly, biochars combined with YIG nanocrystals with different contents and shielding effectiveness of the composites were investigated. The electromagnetic effectiveness of the samples was investigated within the X band (8–12 GHz). The findings indicate that biochar demonstrates enhanced absorption properties with elevated pyrolysis temperatures. Biochars demonstrated an approximate 40 dB shielding effectiveness, while YIG exhibited approximately 7 dB, corresponding to absorption at 8 GHz. However, the combination of biochar and YIG exhibited exceptional absorption, reaching 67.12 dB at 8 GHz.