The grain size of MOCVD-Pb(Zr,Ti)O-3(PZT) thin films was successfully controlled by changing the grain size of Ir bottom electrodes and by changing the growth rate of PZT films. In Zr/PZT/Ir/SiO2/Si capacitors, the grain size of PZT thin films increased from 120 to 240nm as the grain size of bottom Ir electrodes increased from 50 to 200nm. The dielectric constants of PZT thin films increased from 760 to 1440 as the grain size increased from 120 to 240nm. Remanent polarization increased and coercive field decreased as the grain size increased. This dependence of electrical properties on the grain size coincided with that of ceramics.