Lanthanum-modified lead zirconate titanate (PLZT) ceramics possess photostrictive effect that is applicable to photo-driven and wireless actuators. The photo-induced strain is expressed in a product of piezoelectric constant and anomalous photovoltage, and it is theoretically explained that grain size reduction enhances photovoltage. Finegrained PLZT ceramics that have mean grain sizes of 2.0-0.2μm were prepared through the mechanical alloying (MA) synthesis and normal or hot-press sintering process. Their piezoelectric constant, dielectric constant and electric resistivity up to a grain size of 0.5μm were not dependent on grain size and agreed with the conventional one. The photovoltage significantly increased with a decrease in grain size. These results suggested that a lowering of grain size by MA leads to a remarkable improvement of the photo-induced strain value without a decline in strain response. However, the photo-induced strain value within grain size less than 0.5μm extremely declined due to a little remnant polarization. The photo-induced strain with illumination of 15mWcm^-2 intense was maximally estimated to be 1×10^-4.