A flexible ligand docking protocol based on a divide-and-conquer strategy is investigated. This approach first separates total search space into conformation and orientation space. It uses a grid-based method to sample the conformation of an unbound ligand and to select the low-energy conformers. Rigid docking is then carried out to locate the low-energy binding orientations for these conformers. These docking structures are subsequently subjected to structure refinement including molecular mechanics minimization, conformational scanning at the binding site and a short period of molecular dynamics-based simulated annealing. This approach has been applied to twelve ligand-protein complexes with three to sixteen rotatable bonds. The docked lowest-energy structures have root mean square deviations ranging from 0.64 A to 2.01 A with respect to the corresponding crystal structures. The effect of atomic charges and van der Waals parameters on the docking results, and the role of the dielectric constant in the conformation sampling are discussed in detail. A fragment-based docking approach that takes advantages of the divide-and-conquer strategy has also been explored and the results are compared with those produced by a whole molecule-based approach.