The increment of pore pressure Δu and axial deformation Δd of compacted tuff at different compaction works was experimented in triaxial cells applied with isotropic compression pressure σc at undrained condition. After this process, Δu and Δd were measured at drained condition. From these experiments, the following results are obtained. (1) The increment of pore pressure Δu are less than 10 to 30% of σc at moisture content from dry side to 1% wet side of optimum moisture content Wopt. (2) Seepage of water through specimem in two days has scarcely effect on Δu, but Δu is increased to 50% Of σc under the condition of seepage in two weeks. (3) Fore pressure of unsoaked specimen which water content is dry side of Wopt dissipates in one minute, but axial deformation is gradually increased and secondary compression is separated apparently from primary compression.