Magnetic properties of Nd 3%x Bi x Fe 5 O 12 (0 : x : 3) films prepared by metal organic decomposition on Gd 3 Ga 5 O 12 (100) substrates have been investigated. The Faraday rotation angle θ F increased with bismuth concentration. The uniaxial anisotropy constant K u , cubic magnetocrystalline anisotropy constant K 1 , gyromagnetic ratio γ, g-factor, and FMR line width ΔH were determined by ferromagnetic resonance measurements. K u was positive and K 1 was negative for all samples. K u decreased from 9.83 ' 10 4 to 2.05 ' 10 4 erg/cm 3 as x increased from 0 to 3. K 1 was almost constant irrespective of x, and it took a value between %3.28 ' 10 4 and %2.08 ' 10 4 erg/cm 3 . γ, g-factor, and ΔH also decreased with increasing bismuth concentration. From the results of the investigation of the in-plane tensile strain applied to the films, the effect of strain on K u is considered to be small.