Contact angle hysteresis of polystyrene and four modified polystyrenes, containing polar sulfonic acid and carboxylic acid groups, have been evaluated in a two-phase liquid system. Water contact angles have been measured in octane and octane contact angles have been measured in water. It has been demonstrated that wetting characteristics of polystyrene modified with sulfonic acid and carboxylic acid groups can be reversely triggered from polar in the presence of water to non-polar in the presence of octane. A contact angle hysteresis varying from 7 to 88 degrees has been observed and a relationship between the contact angle hysteresis and the polymer surface polarity has been established. The fast kinetics of the wetting transition indicates that such polymers can permit external stimuli-induced modulation of their structures.