In this paper, nanocluster formation behavior in Al–Mg–Si alloys with different Mg and Si concentration was studied by differential scanning calorimetry (DSC), micro-Vickers hardness and electrical resistivity measurements. Two exothermic peaks were detected in the alloys with different Mg and Si concentration in the DSC results, and separated using the Gaussian function method in order to analyze the Cluster (1) and Cluster (2). It is found that both of Cluster (1) and Cluster (2) formation are enhanced with the higher Mg + Si and the Mg/Si ratio close to 1.0. Especially, it is suggested that the formation sequence of Cluster (1) during natural aging is classified into three regions from the results of hardness and electrical resistivity measurement. These results mean that the composition of Cluster (1) is initially Si-rich then gradually becomes enriched in Mg by the incorporation of Mg. The growth rate of Cluster (1) is not high, whereas of Cluster (2) is higher and the composition becomes Mg/Si ≃ 1.0.