The effect of UV Nd:YAG laser intensity on the conductivity and optical properties of hydrothermal ZnO crystal was studied. Three laser intensities characterizing the change of optical, electrical and morphological properties of the crystal have been revealed. The first is improvement of the crystal quality up to I1=3.2 MW/cm2. The second is at laser intensity higher than I2=249.0 MW/cm2 when the formation of cracks takes place. The third I3=290.0 MW/cm2 leads to the formation of “black ZnO”, which is caused by the emergence of Zn nanoparticles with size around 20 nm. At the same time conductivity of ZnO crystal continues to increase and exceeds the initial value by 277 times. The change of ZnO crystal optical and electrical properties is explained by generation, redistribution and agglomeration of Zn interstitials.