The present invention is a composition of an agent for treating a precursor of a three-dimensional object for removing a support material from a precursor of the three-dimensional object containing a three-dimensional object and the support material, the composition containing water and a water-soluble compound having a solubility parameter (SP value) calculated by using the Fedors' method of 8 (cal/cm3)1/2 to 13 (cal/cm3)1/2. The present invention can provide a composition of an agent for treating a precursor of a three-dimensional object that is capable of removing the support material quickly and a method for manufacturing a three-dimensional object using the composition of an agent for treating a precursor of a three-dimensional object by a fused deposition modeling system.