The objective of this study is to investigate the joint strength between a newly developed glass-ceramic sealant and metallic interconnect for application in planar solid oxide fuel cells (pSOFCs). A methodology of evaluating the joint strength at room temperature (RT) and 800 °C was developed in testing two types of sandwich-like specimens under shear and tensile loading. Effects of number of sealant-spreading side and aging treatment on the joint strength at RT and 800 °C were studied. Regardless of the testing temperature and loading mode, the joint strength of specimens with two sides of glass-ceramic sealant was greater than that of single-side ones due to a better wetting effect. An aging treatment at 800 °C for 250 or 500 h degraded the shear joint strength at 800 °C by 17%. A longer aging time of 1000 h further reduced the high-temperature shear joint strength by a slightly additional extent from 17% to 19%.