The soft magnetic properties of nanocrystalline Fe–Nb–B and Fe–Nb–B–P alloys produced in the atmosphere by a melt-spinning method have been investigated. The nanocrystalline Fe_100−x−yNb_xB_y ternary alloys show good soft magnetic properties, relative permeability (μ^′) above 35000 at a frequency of 1 kHz and coercive force (H_c) below 5.0 Am⁻¹, as well as high saturation magnetic induction (B_s) above 1.55 T in the compositional range of x=6.5–6.7 and y=9.3–10.0 at%. The soft magnetic properties of the nanocrystalline Fe–Nb–B ternary alloys are improved by 0.5–1.5 at% substitution of P for B, without decreasing their B_s. The magnetostriction (λ_s) value increases and the mean grain size of bcc-Fe phase (D) decreases slightly by substitution of P for B . The nanocrystalline Fe₈₄Nb_6.5B₉P_0.5 and Fe₈₄Nb_6.5B_8.5P₁ alloys show good soft magnetic properties, μ^′ of 46000–47000 at a frequency of 1 kHz, H_c of 3.6–3.9 Am⁻¹ and the core loss of the 0.09 Wkg⁻¹ at maximum induction (B_m) of 1.33 T and a frequency of 50 Hz as well as high B_s of 1.60 T, suggesting that these nanocrystalline Fe–Nb–B–P alloys are suitable for a core materials for pole transformers.