The effect of the prior austenite grain size (PAGS) on the tensile properties and hole expansion ratio (HER) has been investigated. Starting from different PAGS values (4.7 lm and 15.2 lm) obtained by controlling the austenitizing temperature, microstructure consisting of martensite and austenite (Vc of 0.09–0.18) was produced by the quenching and partitioning process. Increasing Vc had a beneficial influence on the tensile elongation regardless of the PAGS, but deteriorated the HER. However, larger PGAS alleviated the degradation of the HER. The major influence of a larger PAGS on the HER results from the decreased population of interface between neighboring martensite in the shear-affected zone, because that interface is revealed to be a major site for void formation during hole expansion testing.