In this paper, we propose a quality-based use case refinement approach. It consists of a step by step refinement process that combines quality metrics with use case transformation rules. We propose several quality metrics, based on complexity concepts, aimed at measuring the complexity of use cases. Starting from an initial use case, we apply successively a set of transformation rules and measure the resulting use case based on the quality metrics. Our approach is embedded in a general framework allowing us to guide software designers by the mean of quality metrics.