Al-Zn-Mg-Cu alloys are widely used to prepare aerospace lightweight structures owing to their excellent specific strength and damage tolerance. Their performance depends mainly on the high-density nanoprecipitates formed during artificial aging. However, natural aging after solution quenching changes the evolution path of the precipitates, affecting the subsequent artificial aging process. Currently, there is still considerable controversy regarding the impact of natural aging on the peak strength of these alloys after artificial aging. Therefore, this study investigated the contradictory effects of natural aging on the peak-aged strength of Al-Zn-Mg-Cu alloys after artificial aging. Using a newly developed ultrahigh-strength aluminum alloy, namely Al-9.8Zn-2.23Mg-1.38Cu-0.11Cr-0.1Zr (mass fraction, %), the effects of natural aging on precipitate evolution, solute element distribution, and mechanical properties in the peak-aged state were systematically explored. The results showed that natural aging accelerated the response of the material to subsequent artificial aging. The peak strengths after 0, 1, 7, and 30 d of natural aging and artificial aging were (708 ± 4), (685 ± 3), (712 ± 1), and (722 ± 1) MPa, respectively, exhibiting a trend of initial decrease followed by an increase. This behavior was attributed to the formation of Guinier-Preston I (GPI) zones (1.1-1.7 nm in diameter) during short-term natural aging (1 d), which partially dissolved during artificial aging. This reduced the number density of subsequently formed GPI zones, Guinier-Preston II (GPII) zones, and η′ phases and promoted their coarsening. In contrast, prolonged natural aging time increased the proportion of GPI zones, with sizes exceeding the critical nucleation threshold at artificial aging temperatures, facilitating the formation of finer and more dispersed precipitates during subsequent peak aging. Further, this led to a gradual increase in the proportion of GPII zones and decrease in the proportion of the η′ phase. Compared to the peak-aged sample naturally aged for 1 d, the sample naturally aged for 30 d exhibited an approximately 20% increase in the precipitate number density. In addition, the compositional gradient within precipitates of similar size became less pronounced, with significantly reduced maximum concentrations of Zn, Mg, and Cu.