Dual　precipitation　in　a　microalloyed　Al-2.4　wt%　Cu-0.1　wt%　Sc　alloy　was　investigated　in　comparison　with　single　precipitation　in　binary　Al-2.4　wt%　Cu　and　Al-0.1　wt%　Sc　alloys,　respectively.　Although　Al3Sc　nanoparticles　are　more　readily　produced　at　higher　aging　temperatures　in　the　binary　Al–Sc　alloys,　the　Al3Sc　precipitation　in　the　Cu-added　ternary　alloy　was　completely　suppressed　at　723　K　while　unexpectedly　promoted　at　573　K-aging.　Meanwhile,　a　significant　Sc-dependence　of　θ′　precipitation　was　also　evidenced　in　the　573　K-aged　Al–Cu-Sc　alloy　that　the　thickness　of　θ′　precipitates　kept　almost　unchanged　even　to　prolonged　time,　resulting　in　a　high　aspect　ratio　of　＞200　for　the　θ′　precipitates.　The　complex　precipitation　behaviors　are　rationalized　in　terms　of　strong　interactions　between　the　Sc　and　Cu　solutes,　which　could　be　tailored　to　optimize　the　Al3Sc　+　θ′　dual　precipitation　and　hence　to　improve　mechanical　properties.　Moreover,　the　Sc　atoms　fully　stabilized　in　Al　solid　solution　by　Cu　solute　at　723　K　was　discussed,　and　the　high　strength　in　Al–Cu-Sc　alloy　with　dual　precipitation　was　evaluated　by　quantifying　the　strengthen　contribution　from　different　strengthening　mechanism.　©　2021