Ferroelectricity of Pb(ZrxTi1-x)O-3 (PZT) thin films prepared on (001)SrRuO3//(001)SrTiO3 substrates was investigated by changing the Zr/(Zr + Ti) ratio in the film. (001)- and (100)-oriented tetragonal and (10 0)-oriented rhombohedral PZT films were epitaxially grown. Spontaneous polarization (P-s) and coercive field (E-c) values had minimum near the Zr/(Zr + Ti) ratio of morphotropic phase boundary and the latter decreased with increasing the Zr/ (Zr + Ti) ratio. The Zr/(Zr + Ti) ratio dependence of P-s and E-c was in good agreement with the estimation from the crystal symmetry. (C) 2002 Elsevier Science B.V. All rights reserved.