The effect of humidity on subcritical crack growth of indentation crack in lead zirconate titanate (PZT) ferroelectric ceramics under various sustained electric field has been investigated. The results showed that subcritical crack growth of indentation crack could occur in humid air of 60% RH without electric field but did not in air with RH <= 30%. The subcritical crack growth could occur in vacuum under a sustained electric field of E/E-C = 0.14. The incubation time decreased and the amount of the subcritical crack growth increased with increasing the humidity under the sustained field. The threshold electric field for subcritical crack growth decreased with increasing the humidity. (C) 2009 Published by Elsevier B. V.