The effects of grain size on nonlinear dielectric properties of as-deposited SrTiO3 (STO) thin films were studied by using interdigital capacitor. C-axis-oriented STO thin films with different grain size were deposited onto interdigital electrodes made from YBa2Cu3O7 x thin films by pulsed laser deposition (PLD) technique. The grain size of as-eposited STO thin films increased with substrate temperature, and reached a maximum value at 700 8C. With further increase of substrate temperature, the grain size decrease rapidly because of the negative oxygen supersaturation and the high nucleation density. The nonlinear dielectric properties measurements showed to be highly correlated with the grain size of STO thin films; the zero-bias dielectric constant, the dielectric dissipation, and the tunability decreased with the decrease of the grain size.