We present a comparative study of electronic structure and magnetic properties of Gd5Si4 and Gd5Ge4 compounds using ¯rst principles full potential linearized augmented plane wave (FP-LAPW) method based on den-sity functional theory (DFT) using the WIEN2k code. The local-spin density approximation with correlation energy (LSDA+U) method has been used as the exchange-correlation potential. The optimized lattice constants are in good agreement with the experimental data. The total and partial density of states (DOS) of Gd5Si4 and Gd5Ge4 show the di®erence in Si 3p-Gd 5d and Ge 4p-Gd 5d hybridization, which have an e®ective role in indirect exchange interaction. In addition, the magnetic moments of Gd, Si, and Ge atoms and the compounds are calculated to clarify the di®erences in the magnetic properties of these compounds.

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