Modeling heat transfer during friction stir welding (FSW) process is crucial for understanding welding mechanism and optimizing process parameters. Since heat transfer is usually accompanied with the material flow in FSW, the meshless method, which can easily treat large deformation in a Lagrangian framework, is promising for FSW modeling. In this paper, we develop a meshless particle method for the analysis of transient heat transfer during FSW process. In the developed method, a heat source model based on sticking friction is implemented to describe the heat generation of FSW. A particle approximation with first-order consistency is employed to discretize the governing equation of heat transfer. A penalty method is proposed to impose different thermal boundary conditions, and a smoothing algorithm is introduced to enhance numerical stability. Two examples are firstly given to verify the accuracy and parametric effect of the meshless particle method. The method is then used to simulate heat transfer during FSW of 12.7 mm-thick A16061-T6 plates. The calculated temperature distributions are presented and compared with those computed by FEM. The obtained thermal cycles are found to be in good agreement with those obtained from experiments. The validated model of FSW of A16061-T6 plates is then employed to predict the maximum temperature, heat generation rate and torque for various welding parameters and tool dimensions. (C) 2016 Elsevier Ltd. All rights reserved.