Measurements have been made at room temperature of the strength and fracture toughness of a complex nicker silicide containing particles of a ductile phase. The matrix was either a single-phase L1(2) distorted Ni3Si (beta(2)) or a two-phase Ni3Si (beta(1)) and Ni31Si12 (gamma) mixture. The particles were a solid solution of Ni(Si) encased within a rim of beta(1); they contained a dispersion of beta(1) precipitates. The principal variable was the particle size, and this had little effect on the properties. The results show that the compressive yield strength (similar or equal to 1200 MPa), the compressive ductility (2-10%) and the fracture toughness (17 +/- 3 MPa m(1/2)) are relatively high. The toughness and ductility are attributed to the plastic deformation and ductile fracture of the crack-stopping Ni(Si) particles.