FLAVIN-BINDING KELCH REPEAT F-BOX 1 (FKF1) encodes an F-box protein that regulates photoperiod flow-ering in Arabidopsis under long-day conditions (LDs). Gib-berellin (GA) is also important for regulating flowering under LDs. However, how FKF1 and the GA pathway work in concert in regulating flowering is not fully understood. Here, we showed that the mutation of FKF1 could cause accu-mulation of DELLA proteins, which are crucial repressors in GA signaling pathway, thereby reducing plant sensitivity to GA in flowering. Both in vitro and in vivo biochemical anal-yses demonstrated that FKF1 directly interacted with DELLA proteins. Furthermore, we showed that FKF1 promotedubiquitination and degradation of DELLA proteins. Analysis of genetic data revealed that FKF1 acted partially through DELLAs to regulate flowering under LDs. In addition, DELLAs exerted a negative feedback on FKF1 expression. Collectively, these findings demonstrate that FKF1 promotes flowering partially by negatively regulating DELLA protein stability under LDs, and suggesting a potential mechanism linking the FKF1 to the GA signaling DELLA proteins.