Core deflection in powder injection molding is one of the main causes of the structural defects in the molded part. Simulation of the core deflection in the injection molding process requires solution of the fluid-solid interaction problem, in which the fluid flow and solid deformation problems are coupled along the fluid-solid interface. A three-dimensional finite element program was developed in this work for a non-isothermal injection molding simulation including the fluid-solid interaction effects. With the assumption of small deformation in the solid structure, the fluid flow problem is formulated in an Eulerian frame-work, whereas the solid structure problem is formulated in a Lagrangian framework. Numerical simulation of the filling stage of injection molding for an airfoil-shaped part is presented and compared with the experimental data. The predicted melt-front advancement as well as the pressure is in good agreement with the corresponding experimental results. The predicted core deflection during the filling stage of the injection molding process is also compared with the measurements on a molded part.