Nanocomposite Nd3.6Pr5.4Fe83Co3B5 ribbons were prepared by direct melt spining at wheel speed of 20m/s. Although Nd2Fe14B-type phase and α-Fe were found in the ribbons, a single hard magnetic behavior with high coercivity can only be found in the hysteresis loop. The recoil curves show a comparatively high degree of reversibility in the fields below coercivity. From the investigations of reversible and irreversible portions in DC demagnetization remanence curve, the irreversible nucleation field of about 440 kA/m has been obtained in melt-spun Nd3.6Pr5.4Fe83Co3B5 ribbons. The measurements of magnetic viscosity show that the time-dependent magnetization changes are associated with reversal of the hard phase. The thermal fluctuation field of about 2.0kA/m was obtained.