Nowadays, the interest about the implantable or wearable devices has increased rapidly. Due to these attentions, it becomes greatly important issue to develop long-term powering and recharging of implantable devices through a safe, efficient and convenient way and there have been several developments about power sources for implantable devices such as batteries, nuclear cell, bio-fuel cell, etc. Especially, a glucose fuel cell can be a promising candidate for replacing batteries because it uses glucose attained by body fluids as fuel and shows long-term stability and adequate power density. This paper is focuses on investigating the effects of electrolyte membrane characteristics on the glucose fuel cell. Commercially available Nafion membranes with various different thicknesses were characterized by measuring and analyzing electrical power generation quantitatively. The characterization suggests that thinner Nafion membrane led to better performance (higher peak power, low ohmic loss and low activation loss) than thick one, but too thin membrane shows low performance due to the lack of stability stemming from fabrication failure