An electric field was applied across a deionized water droplet placed on a multi-walled carbon nanotube (MWCNT) membrane. Droplets of different size were tested by varying the voltage applied from 3 to 25 V during the electrowetting process. After electrowetting, it was observed that the topography of the membrane deformed from vertical alignment to a grouped pattern due to bubbles appearing during the electrowetting process, indicating the occurrence of electrolysis. For the droplet size ranging from 2 to 3.5 mu l, the contact angle (CA) for smaller droplets reduced more dramatically than for larger droplets at the same voltage, and the contact angle saturation condition also varied in response to the droplet size. To reveal the droplet size effect, the Young-Lippmann equation is modified to simulate CA reduction on a MWCNT membrane.