Abstract: The present invention discloses a workflow mining system which can evaluate, analyze and determine previous execution results of processes or activities by applying a data mining technique to workflow log data accumulated during the operation of a workflow system, and a method therefor. The workflow mining system extracts necessary data from a database of a workflow server, generates an analysis table, performs a preprocessing process for removing unnecessary attributes on the basis of the extracted data or converting a digital variable into a symbolic variable, and analyzes a decision making tree or association by using the preprocessed data. C4.5 algorithm is used for the decision making tree analysis and Apriori algorithm is used for the association analysis.