GAMER is a GPU-accelerated Adaptive MEsh Refinement Code for astrophysical applications. Currently the code solves the hydrodynamics with self-gravity. By taking advantage of the extraordinary performance of GPUs, up to two orders of magnitude performance speed-up has been demonstrated in comparison to the CPU-only performance. Currently the code supports the following features: Adaptive mesh refinement (AMR); Hydrodynamics with self-gravity; A variety of GPU-accelerated hydrodynamic and Poisson solvers; Hybrid OpenMP/MPI/GPU parallelization; Concurrent CPU/GPU execution for performance optimization; Hilbert space-filling curve for load balance