Changing market environment, increasing global competition and fluctuating customer demands require efficient operation of production and logistical processes. The essence of Lean manufacturing is the cost reduction and improvement of productivity. There are lots of Lean methods for improvement of the production performance. The paper shows the essence, characteristics and advantages of application of Lean production philosophy. The article describes the theoretical background relating to the process improvement and a practical design method is also introduced in a case study. This case study which is a part of a real R+D project shows how can be improved the efficiency of a real assembly line by application of 4 Lean methods: Takt-time analysis, Line balance, Cellular design and One-piece flow.