Prediction of fault proneness of modules in software is one of the ways to ensure the achievement of software quality and reliability. Software delivered cannot not always be bug free, the more the number of bug the more the dis-satisfaction among client due to degradation in software quality and reliability. Though we have few models for detecting software fault prone modules, the intend of our work is to increase the reliability of the software by using an approach named Rough Fuzzy c-means (RFCM) clustering algorithm to analyse the fault proneness of the software modules under test. This helps in an efficient analysis of the modules having an ambiguous behaviour using rough set boundary which is not possible using traditional clustering methods. A dataset from PROMISE software engineering repository has been taken for the experimental analysis. The results were promising enough to determine software modules which fall in the boundary region of ambiguity emphasizing the software team to focus on those modules to achieve higher reliable system.