This report summarizes the results of X-ray diffraction analyses of core samples from Integrated Ocean Drilling Program (IODP) Sites C0011 and C0012, offshore southwest Japan. We analyzed 211 specimens (<2 µm size fraction) recovered during IODP Expedition 333. Most of those samples come from the uppermost hemipelagic/pyroclastic facies (Unit I) of the Shikoku Basin, with a limited number from the volcanic turbidite facies (Unit II) and the pelagic clay facies (Unit V). Minerals of the smectite group are generally the most abundant. At Site C0011, the amount of smectite in the clay-size fraction of Unit I averages 40.8 wt% (standard deviation = 11.5) and increases downsection. Proportions of illite and chlorite average 36.4 and 15.5 wt%, respectively. Average contents of kaolinite and quartz are 3.6 and 3.7 wt%, respectively. At Site C0012 (Unit I), the amount of smectite averages 50.0 wt% (standard deviation = 13.5) and increases downsection. Averages for the other minerals in the clay-size fraction are illite = 31.8 wt%, chlorite = 10.1 wt%, kaolinite = 5.5 wt%, and quartz = 2.6 wt%. Most values of illite/smectite expandability fall between 60% and 70%, and there are no systematic changes downsection. Values of the illite crystallinity index are generally consistent with detrital sources that were exposed to anchizone metamorphic conditions.