Disclosed is an aluminum alloy sheet resistant to deterioration through natural aging. The aluminum alloy sheet is an Al—Mg—Si aluminum alloy sheet containing 0.35 to 1.0 percent by mass of magnesium; 0.5 to 1.5 percent by mass of silicon; 0.01 to 1.0 percent by mass of manganese; and 0.001 to 1.0 percent by mass of copper, with the remainder being aluminum and inevitable impurities, in which the amount of dissolved silicon is 0.55 to 0.80 percent by mass, the amount of dissolved magnesium is 0.35 to 0.60 percent by mass, and the ratio of the former to the latter is 1.1 to 2. The aluminum alloy sheet may further contain 0.005 to 0.2 percent by mass of titanium with or without 0.0001 to 0.05 percent by mass of boron.