This paper suggests a balanced scorecard (BSC) framework for measuring and evaluating the performance of knowledge workers in professional service firms(PSFs) which are typical knowldege-based organizations. As a strategic learning system, the balanced scorecard allows business leaders to drive and modify their business strategies based on the balanced measurement of key performance indicators(KPIs), which are basically divided into four domains such as financial achievement, customer orientation, internal business process, and innovation and learning. Conducting a focused case study on performance evaluation of knowledge workers from a balanced viewpoint, we could evaluate their competency and potential in more comprehensive manner. We also employ the analytic hierarchy process (AHP) approach for derive relative weights of key performance indicators and link it to a spreadsheet model for rating the individual performance of knowledge workers in a systematic way.