: The increasing accuracy requirements in many of today’s simulation tasks in science and engineering more and more often entail the need to take into account more than one physical effect. Among these multiphysics problems are fluid-structure interactions (FSI), i.e. interactions of some moving or deformable elastic structure with an internal or surrounding fluid flow. Due to Lagrangian view point and truly meshless formulation of SPH method, it can offer an alternative choice to simulate problems encountered free surfaces, interfaces,and violent surfaces.There are also two main strategies for dealing with the interfaces in FSI problems, i.e. segregated and coupled strategy. The first approach is the easiest one. In segregated strategy, the governing equations are integrated sequentially in each media and therefore, the effects of each phase on the other one have a lag through time stepping. On the other hand, in coupled approach the governing equation are integrated simultaneously and the problem domain is considered as a unified system. In this study the SPH method with coupled strategy are chosen to integrate governing equations for the FSI problems. An algorithm is developed which is capable of dealing with large deformations and high density ratios. In this study fluid is considered to behave as a Newtonian viscous fluid and solid is supposed to be an elastic body with large deformation. To validate the algorithm, first three problems with the presence of only a single phase, solid or fluid, are considered. These include the free deformation of a fluid patch in a void, the dam breaking test case and the free vibration of a cantilever beam. Numerical results show that the algorithm can accurately predict single phase problems with violent deformation at the surfaces. Then the algorithm is applied to two FSI problems. As the first FSI test case, an elastic bed lid driven cavity is considered and its results are compared with the results obtained by a FEM approach. A parametric study of solid and fluid properties is performed to investigate the behaviors of proposed algorithm in different density ratios and deformation rates. Finally, the last test case is devoted to the problem of an oscillating cantilever beam in a confined and unconfined fluid. Conclusion: A coupled algorithm has been proposed for the FSI problems with large deformation and density ratio using SPH method to integrate governing equations in both solid and fluid regions. The capabilities of new method has been shown by simulating several test cases.