The Usuki Stone Buddha Statues in Oita are consisted of 60 Buddhas which represent of Japan carved on the rock-cliff in the 12 to 14th centuries. The basement rock of the statues is dark gray welded lapilli tuff that containing the Aso-4 pyroclastic rock group. Deterioration maps for the Hoki Ⅰ and the Furuzono Buddha Statues group show multi-directional fissures on the Cakra, and sheeting-off zone at the margin of uprising water. Deterioration rate of the Hoki Ⅰ group was calculated fissure about 121 in number, 19% of sheeting-off zone and 51% of biological weathering in surface of area. And the Furuzono group was also evaluated as about 48 of fissures in number, 24% of sheeting-off zone and 41% biological weathering. The slope stability assessment results, the Hoki Ⅰ developed discontinuous planes has possibility of planar, toppling and wedge failures in all caves. Ultrasonic velocity of the Aizen-myooh (basement rock) ranges from 1,520 to 2,794 (average 2,298㎧). And pedestal of Amita-yeorae which has been replaced by new fresh rock is measured as 3,242 to 4,141 (average 3,813㎧). Therefore, we establish of planing conservation treatment and reinforcement methods to fissure, cavity, sheeting-off zone in the Buddha surface.