We present a new real-time method that can animate a moving elastic object that could collide with other objects in a virtual environment. For simulating physical motions of elastic objects, we exploit a Boundary Element Method (BEM), which can achieve efficient computations and desired deformation as opposed to spring models and a Finite Element Method. In case that real-time processes are required for the BEM, only the physical simulation cannot achieve animations; therefore, this paper proposes a 2D model that is combined with the BEM. Since it is difficult to animate 3D elastic objects in real-time, we propose a method that approximates the 3D motions based on the 2D model. The effectiveness of the proposed method is demonstrated by the experiments in which the dynamical behaviors of a jelly are reproduced in a virtual environment in real-time. Key words: elastic object, boundary element method, real-time animation, physical simulation