This paper describes effects of micro-square-shaped pillar array structures and chemical modification by SF₆ or O₂ plasma irradiation on wetting properties of SU-8 (photosensitive epoxy resin) for water. Contact angles were measured and microscopic observation of water droplet contours were conducted through the bottom of the glass substrate. For the SU-8 surfaces without chemical modification, Wenzel mode wetting occurred constantly. However, because of the pinning effect, the contact angles on surfaces with micro structures were larger than the values calculated based on the Wenzel mode wetting. The SU-8 surfaces modified by SF₆ plasma showed Cassie mode wetting generally and remarkable hydrophobicity with large contact angles of more than 150 deg. The surface became super-hydrophilic after O₂ plasma modification.