Business leaders understand the strengthg and usefulness of managing the improvement of business results through process improvement teams. There is no better approach to process improvement than the application of Six Sigma tools and methods. Moreover, the disciplines of project management and Six Sigma are substitutes but they are complementary. The similarities between project management and Six Sigma include:

• Utilization of established project management techniques to efficiently manage a project and project teams.

• Necessity of proactive project sponsors or champions to help ensure project success.

• Life cycle and phases.

• Need for a well-experienced project facilitator to lead the effort.

Six Sigma adds additional dimensions to project management: 

• Powerful set of process improvement tools.

• Statistical and process thinking to understand and improve results.

• Understanding of variation, to eliminate knee-jerk reactions.

• Quantitative analysis for base decisions on facts and data.

Read more at: 

http://www.microsoft.com/project/en/gb/six-sigma.aspx