Monoclinic zirconia was densified using hot isostatic pressing (HIP) at 1000 °C and 190 MPa for 1 h, using steel encapsulation and boron nitride as protective and release agent. The maximum of the average densities after HIP was 93.4% of theoretical density and the average final grain size was 220±16 nm. However, some regions exhibited nearly full density. X-ray Photoelectron Spectroscopy (XPS) revealed carbon contamination, no reduction of Zr4+ and no significant diffusion of boron or nitrogen.