Laser peening has been applied to silicon nitride (Si3N4) ceramics without any pre-coating. X-ray diffraction study revealed that plastic strain was introduced into the surface layer of the ceramics. Compressive residual stress was also imparted, which became larger with increasing peak power density of irradiated laser pulses. Surface roughness significantly increased due to ablative interaction of the surface with laser pulses. A Weibull plot of four-point bending test results clearly showed the increase of the bending strength and Weibull modulus by laser peening in spite of the increase of the surface roughness.