A new miniature DMFC system that includes a fuel cell stack, a fuel tank and a passive ancillary system (termed “thermal-fluids management system” in this paper) is presented. The thermal-fluids management system utilizes passive approaches for fuel storage and delivery, air breathing, water management, CO2 release and thermal management. With 5.1g of neat methanol in the fuel cartridge, a prototype has successfully demonstrated 18h of continuous operation with total power output of 1.56Wh.