Metal-ceramic composites exhibit desirable combinations of materials properties, but are limited by the complexity of processing, particularly for metal-ceramic nanocomposites. The in situ partial reduction technique is a simple processing method that can be used to produce tailorable metal-ceramic composite microstructures. In this work, in situ partial reduction was utilized to generate novel Co-Ti (x) O (y) composites, including nanocomposites, through the reduction of CoTiO3. By modifying the temperature (800-1400 A degrees C) and time (1-8 h) of reduction, composites with varying cobalt particle size and cobalt grain size were fabricated. Differences in the cobalt crystal structure and nature of the titanium oxide phase were also observed. The lowest-temperature heat treatments resulted in metal-ceramic nanocomposites. The Co-Ti (x) O (y) composites were characterized through scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction. The effect of processing variables on the properties of the composites was evaluated through nanoindentation of the embedded cobalt particles, and it was found that cobalt particle hardness is strongly correlated with grain size. The many useful properties of cobalt and titanium oxide, in conjunction with the range of controllable microstructures, demonstrate that the in situ partial reduction technique has excellent potential for metal-ceramic composite production.