In this work a simple method to phosphorize the surface of nanometric particles of crystalline zirconia is described. The reaction rate of phosphorization was regulated by adding acetic acid and the observed particle size was in the range 40–60 nm. A proton conductivity of the order of 10−3 S cm−1 was measured for phosphorized nanoparticle powder mixed with micro-fine teflon powder (3:1) at room temperature. Phosphorized nanoparticles are stable when dispersed in acetic acid and are suitable for composite material preparation. Copyright © 2005 John Wiley & Sons, Ltd.