The effect of Zn addition on clustering behavior in a pre-aged Al-Mg-Si-Cu alloy and its relation to bake hardening response are investigated. After pre-aging at 100 °C for 3 h, the Zn addition prompts the formation of clusters with a uniform Mg/Si ratio, which can easily transform into β" phases. Consequently, a fine and dense distribution of β" phases is observed in the Al-Mg-Si-Cu alloy with Zn addition during bake hardening treatment at 185 °C for 25 min after pre-aging. This correlates well with the enhanced bake hardening response of the Al-Mg-Si-Cu alloy with Zn addition.