Software maintenance activities often cause design erosion and lead to increased software complexity and maintenance costs. Extract Class Refactoring attempts to address design erosion by identifying and pulling out extraneous functionalities from a class and distributing them to new classes. This thesis extends previous research in this area by improving a metric known as Structural Similarity between Methods (SSM) used during Extract Class Refactoring. The improved metric, called Variable based Similarity between methods (VSM), establishes similarities between methods based on the variables they share, and on how they use these variables. Strongly connected methods are then allocated into new classes. The thesis also introduces another metric, Cognate Members Metric (CMM), which identifies those members of a class that are only used in combination with each other, and hence, probably belong together in a separate class. Additionally, this work extends and modifies existing refactoring processes for extracting classes. A software prototype that performs Extract Class Refactoring has been developed to substantiate the research. A few Case studies are discussed and comparison and analysis of results of refactoring using the new and older approaches of the Extract Class Refactoring process are presented.