The marked optical damage was observed in thin Z-cut plates of the deeply reduced nominally pure LiNbO3 crystals, when a 514.5-nm-laser beam with ordinary polarization was focused on the ±Z face. The longitudinal photovoltaic and pyroelectric effects are shown to be responsible for most of the important peculiarities of the optical damage dynamics. The anisotropy in the behavior between the +Z and −Z faces has been explained by interference of the different kinds of pyroelectric and photovoltaic effects to the space-charge field with an altering relative sign.