Single-phase filled skutterudite compounds BayNx Co4-xSb12 (x=0-0.1, y=0-0.4) were synthesized by a two-step solid state reaction. Effects of Ba filling fraction and Ni content on the thermoelectric properties of n-type Ba yNixCo4-xSb12 were investigated. Thermal conductivity decreased with increasing Ba filling fraction and temperature. When barium filling fraction (y) was fixed at 0.3, the thermal conductivity decreased with increasing Ni content, and reached a minimum value at about x=0.05. Electron concentration and electrical conductivity increased with increasing Ba filling fraction and Ni content. Seebeck coefficient increased with increasing temperature, and decreased with increasing Ba filling fraction and Ni content. A maximum ZT value of 1.2 was obtained at about 800 K for Ba 0.3Ni0.05Co3.95Sb12.