Ti-28 at.%Ta powders were produced by rapid solidification via plasma rotating electrode process (PREP). It is found that microstructure, morphology and phase constituents of Ti-28Ta powders are particle size dependent. Small powder particle exhibit the formation of predominant martensitic α” and minor metastable β, whilst large particles consist of primary metastable β with minor martensitic α” phase. The amount of martensitic α” increases while the amount of metastable β phase decreases with decreasing the particle size. The martensitic α” lath with the size of about 50 nm wide and 1 μm long are formed preferentially at the β grain boundaries. The martensitic transformation start temperature (Ms) and peak temperature (Mp) are ∼390 °C and ∼340 °C respectively for the Ti-28Ta powders with the particle size between 40 and 65 μm. An increased Vickers micro-hardness is obtained and is associated with decreasing particle size. •We investigated the particle size effect on the microstructures of the Ti-28Ta powders.•The cooling rate has a significant effect on α”/β ratio in powders dependent on the particle size.•The α” martensitic plates were preferentially formed at the grain boundaries.