This report documents the results of constant-flow permeability tests in the vertical (along core) direction administered at effective isotropic confining stresses of 0.28 MPa (40 psi) and 0.55 MPa (80 psi). Specimens from the Nankai accretionary prism were collected from Hole C0002P of the Integrated Ocean Drilling Program. Beds dip at steep angles (typically 80° or more) throughout the cored interval (2174.98–2209.64 meters below seafloor). We tested specimens that consist of indurated clayey siltstone and medium to coarse siltstone. Environmental scanning electron microscopy shows that grain fabric is random and does not vary significantly among the specimens tested. Hydraulic conductivity values range from 3.83 × 10–9 to 2.68 × 10–8 cm/s. Intrinsic permeability values range from 3.80 × 10–18 to 2.66 × 10–17 m2.