The crystallization behaviour, electrical resistivity, magnetic and mechanical properties of as-quenched bulk amorphous Fe72Si 4B20Nb4 alloy was investigated. The alloy, prepared in the form of rods by a copper mould casting technique, revealed an amorphous structure as observed from x-ray diffractometry. Differential scanning calorimetry and thermal variation of electrical resistivity measurements showed distinct glass transition temperature, Tg occurring 50-60 K below the crystallization onset (TX). Such a wide supercooled range was also attributed to the highly reduced glass transition temperature, T rg which was in the range of 0.56-0.58 found to be prevalent in good glass forming alloys. The alloy also showed a non-linear decrease in stability time at different temperatures between Tg and TX. The bulk amorphous alloy exhibited a drastic decrease in electrical resistivity around the glass transition temperature which was attributed to high electron propagation due to enhanced stress relaxation as result of a decrease in viscosity. The material exhibited superior soft magnetic properties with a coercivity value of 212 mOe, which is fairly low with respect to reported bulk amorphous alloys. The amorphous alloy also showed saturation induction of 12 kG and a moderate Curie temperature of 595 K. The as-quenched bulk amorphous alloy exhibited a high mechanical hardness of 1250 HV (Vickers). The superior soft magnetic properties coupled with high mechanical hardness opens up the scope for bulk amorphous Fe-Si-B systems with Nb incorporation. © 2006 IOP Publishing Ltd.