Constant extension rate tests were conducted to determine the effects of environment and polarization potential on the stress corrosion cracking (SCC) behaviors in the short-transverse direction of wrought high-strength aluminum alloys 7075 and 7475 in thick sections. The specimens in T6 condition of the alloys reveal a noticeable embrittlement due to SCC when tested in laboratory air, and thus it gives misleading results to employ laboratory air as a reference environment for evaluating SCC susceptibility. The susceptibility can be expressed well in terms of the ratio of the elongation to fracture in a corrosive environment to that in dry nitrogen gas. The SCC behaviors in a NaCl solution, greatly depending on the polarization potential, can be classified into the four potential ranges with the modes of corrosion attack. The high-purity alloy 7475 shows a more enhanced SCC resistance than 7075.