This paper presents experimental and numerical investigations on the cross-sectional behavior and compressive capacities of aluminum alloy channel section stub columns after exposure to fire. A testing program was performed, including heating tests, postfire material tests, geometric imperfection measurements, and 16 stub column tests. The testing program was followed by a numerical modeling program. Finite-element models were developed to simulate the test responses and conduct parametric studies to obtain additional numerical data. The obtained test and numerical data were analyzed and adopted to perform design analyses, in which the applicability of the relevant room-temperature design rules in the American, European, and Australian/New Zealand codes to the postfire design of aluminum alloy channel sections under compression were examined. The results of the design analyses reveal that all three examined design codes yield excessively conservative and scattered predictions of postfire strengths, owing to the neglect of significant postfire material strain hardening. Then, a new design approach was proposed by rationally considering the material strain hardening. The new proposal was found to offer greatly improved design accuracy and consistency compared to the American, European, and Australian/New Zealand codes, especially for aluminum alloy channel sections after exposure to elevated temperatures above 400°C.