Nano hydroxyapatite (nHA) zirconia (ZrO2) composites have been produced by spark plasma sintering (SPS). During the SPS process low temperatures (600-950 degrees C) and short dwelling time (5 min) have been applied to avoid the decomposition of nHA as well as the reaction between nHA and ZrO2. The grain size of the sintered composites was between 200 and 1000 nm. Carbon diffusion was induced from the graphite die and layered composite structure was formed. These observations might be related to the spark plasma sintering side effects. The microstructure and mechanical properties of high hydroxyapatite content zirconia composites have been found to be influenced and strongly correlated with the specialties of SPS method. (C) 2013 Elsevier Ltd. All rights reserved.