Electrowetting is a phenomenon that controls the surface tension of droplets by electricity and changes the wettability of the droplets. There are many applications of electrowetting, such as tunable liquid lenses, electronic paper and 3D display. Response time of electrowetting applications is important for them, but the relationship between response time and the physical parameters for electrowetting operation has not been deeply investigated. Therefore, we have investigated the effects of physical properties such as viscosity, interfacial tension and substrate roughness on the response time in AC electrowetting and found the optimal conditions for fast electrowetting. Also, an electrowetting circular lens was fabricated based on the optimal conditions and compared to a conventional electrowetting circular lens for response time. The experiment was conducted on a 0.4 mm thick aluminum plate with a 1μm thin parylene C film deposited with a 50 nm Teflon coating. The experiment results showed that the fastest response time is obtained at 5 mPa∙s conducting liquid (water-glycerol mixture) with 0 wt % SDS (sodium dodecyl sulfate) on default aluminum plate (RMS roughness 270 nm). Through this experiment, it was possible to control the spreading response pattern of electrowetting from under-damped response to over-damped response by changing the conditions of viscosity of conducting liquid, surface tension between two immiscible liquids, and substrate roughness. Also, a critical damping response was implemented using a hardware method by applying the optimum condition without voltage shape variation technology.