To improve slip resistance of a flat flooring without any patterns, we proposed a combination of hydrophobic and hydrophilic treatments and investigated the effect of the combination on slip resistance between a flat glass plate and shoe sole under wet conditions. The concept of the combination is to make the hydrophilic area as a refuge for water films or droplets and increase the real dry contact between the hydrophobic area and shoe sole. The hydrophilic area was a circle shape and was allocated in a grid pattern on the hydrophobic sea while seven types of flat-glass-plate specimens were evaluated. Based on the friction test results, it was indicated that the combination of hydrophobic and hydrophilic treatments improves the slip resistance when the area of hydrophilic island was minute against the hydrophobic sea. From the observation of contact interface, the trend of the shear strength against the hydrophobic area ratio established the effect of the combination.