Provided are an apparatus and method of componentizing a legacy system that reconstructs software components, which are included in the legacy system, as abstract or logical modules according to the association between the components. An apparatus for componentizing a legacy system includes a legacy code analyzing unit which analyzes the association between one or more legacy codes, which are included in the legacy system, a component generating unit which generates data for defining one or more components by referring to the analyzed association, a component analyzing unit which analyzes the association between the components, and a data updating unit which updates the data by referring to the association between the components.