Within the framework of an isospin-dependent quantum molecular dynamics (IDQMD) model, we study systematically the isospin dependence of four main categories of collective motions in intermediate energy heavy ion collisions, i.e., the in-plane directed flow, in-plane rotational flow, out-of-plane squeeze-out flow, and radial expansion flow. In particular, the influence of symmetry energy and isospin-dependent nucleon-nucleon cross sections on the isospin dependence of the collective flows is studied. ©2001 American Institute of Physics.