Submicron electrolyte films are a key component of intermediate temperature solid oxide fuel cells. Several groups have reported size-dependent in-plane ionic conductivity in thin films of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria. Here we report both in-plane and through-plane conductivity of dense YSZ films varying in thickness from 20 to 200 nm. In-plane measurements were performed on YSZ films grown on silicon wafers coated with SiO2 or Si3N4. Detailed structural studies were performed on the YSZ films to investigate crystallinity and uniformity. Micro-fabricated strips with Pt electrodes were used to obtain conductivity vs. temperature from 200 – 600 C in a custom-designed micro-probe station. These films have activation energies from 0.77 to 1.09 eV. Their absolute conductivity is lower compared with other reports, and shows little or no thickness or substrate dependence. Through-plane and fuel cell measurements were performed by depositing YSZ on a nitrided silicon wafer, then etching through the wafer and depositing porous platinum electrodes on both sides. We will discuss the electrochemical conduction studies in detail along with fuel cell performance and correlation with electrode microstructure. The results have potential relevance to fabrication of micro-fuel cells for environmentally friendly portable electricity generation.