Fully dense composite materials of M3/2 high speed steel reinforced with 5, 10 and 15vol. % of high purity niobium carbide were developed using powder metallurgy processing. This work describes and discusses the mechanical behavior of the various composite systems. Mechanical properties were characterized by Rockwell hardness, compression and three point bending tests. It was found that the addition of ceramic particles causes a very small increase in the hardness and 0.2% yield strength, but a decrease in the transverse rupture strength is observed. In order to eliminate the influence of martensite on the mechanical properties, measurements were also conducted after tempering. After this treatment, the reinforced materials showed a moderate yield stress increase at room temperature respect to the unreinforced M3/2. However, the bend strength values were not affected significantly by this treatment. At high temperatures, the addition of reinforcement particles causes a slight increase in the strength. Strain rate-change tests in compression were performed at strain rates ranging from 3 x 10-6 to 2 x 10-3 s-1 in the temperature range from 650 to 750°C. The deformation behaviour was characterized by a stress exponent ranging from 5 to 7 and an activation energy for plastic deformation similar to that found in high alloyed ferritic steels.