This research study is conducted on one bay-one story non-sway frames where the effects of the rotational restraint and slenderness ratio on the post-buckling strength of the axially restraint column under thermal load are studied. Geometric non-linear analysis of the structures is performed using a research program based on the beam-column theory. A total 32 models are created considering two different bottom end conditions: fixed and hinged, slenderness ratios: 50 and 125, and the beam to column length ratios: 0.5,1,1.5 and 2, to account for the variation in the rotational restraint. All models are subjected to thermal loads and numerical results are obtained to study the post-buckling behavior of the columns of the frames under thermal loads.