Heat stress (HS) caused by ambient high temperature pose a threat to plants. In the natural and agricultural environment, plants often encounter repeated and changeable HS. Moderate HS primes plants to establishment of a molecular ‘thermomemory’ that enables plants to withstand a later-and possibly more extreme-HS attack. Recent years, brassinosteroids (BRs) have been implicated in HS response whereas little is known about whether BRs signal transduction modulates thermomemory. Here, we uncover the positive role of BRs signaling in thermomemory of Arabidopsis thaliana. Heat priming induces de novo synthesis and nuclear accumulation of BRI1-EMS-SUPPRESSOR (BES1), the key regulator of BRs signaling. BRs promote the accumulation of dephosphorylated BES1 during memory phase, blocking BRs synthesis impairs dephosphorylation. During HS memory, BES1 is required to maintain sustained induction of HS memory genes and directly targets APX2 and HSFA3 for activation. In summary, our results reveal a BES1-required, BRs-enhanced transcriptional control module of thermomemory in Arabidopsis thaliana.