Forced convection heat transfer from a circular cylinder with a flexible fin in laminar flow with Re = 200 and Pr= 0.7 is investigated numerically. The two-dimensional incompressible Navier-Stokes equations and energy equation are coupled with the Euler-Bernoulli beam equation to describe the flow-induced vibration (FIV) of the flexible fin considering the convection heat transfer process. The modified characteristic-based split scheme, Galerkin finite element method, semi-torsional spring analogy method and loosely coupled partitioned approach are employed irrespectively for the flow and convection heat transfer, fin vibration, mesh movement and fluid-structure interaction. The accuracy and stability of the proposed numerical method are validated using three benchmark models including the forced convection heat transfer from a stationary cylinder, forced convection heat transfer from a transversely oscillating cylinder and FIV of a flexible plate behind a square cylinder. Finally, forced convection heat transfer characteristics from a circular cylinder with a flexible fin with fin length l= 0.5D-1.5D (D is the cylinder diameter) and elastic modulus E =10(4) - 5 x 10(5) are analyzed in detail. The numerical results show that, when the vortex shedding frequency approaches the natural frequency of the flexible fin, the FIV frequency is locked on the natural frequency and the fin exhibits large-amplitude vibration. As a result, the 'dead water' region behind the cylinder is reduced and the convection heat transfer is improved. In the combinations of parameters considered, a maximum of 11.07% enhancement in heat transfer is obtained by the flexible fin. (C) 2018 Elsevier Ltd. All rights reserved.