Amorphous melt-spun ribbons of Pr4.2Tb0.3Fe78B17.5 alloy were consolidated into bulk nanocomposite magnets by Spark Plasma Sintering method. Effect of sintering conditions on the density, microstructure and magnetic properties were studied. Higher sintering temperature improved the densification of the magnets, while deteriorated their magnetic properties simultaneously due to the excess crystal grain growth. Magnet possessed a Br of 1.04 T and a JHc of 220 kA/m under the optimal sintering condition, and its microstructure contained satisfied grains with an average size of about 20 nm.