The effect of ScSZ - YSZ composite on stabilization and electrical conductivity has been investigated. Composite of (8YSZ)x(10ScSZ)(1-x)(x=0~1) were mixed by wet milling process and sintered at 1400°C for 5h and characterized by XRD, SEM, dilatometry and impedance spectroscopy. the long-term stability of the electrolyte materials was examined at 900°C for up to 1000h. The cubic phase shifts from an YSZ character to a ScSZ character with increase in percentage of ScSZ. The conductivity of composite with increasing ScSZ content is slightly higher than YSZ. Especially, above 50wt% ScSZ composition exhibited higher electrical conductivity. All compositions showed conductivity degradation after annealing at 900°C for 1000h.