The main goal of this work is to design an urban bus assembly line and to optimize it using a discrete event simulation software, AnyLogic. The assembly steps are identified and validated by a Spanish manufacturing company and the line has been structured to allows flexibility in terms of output and production mix. The designed layout has been simulated to analyse the line performances and highlight the improvements useful to increase the efficiency. Moreover the required material handling equipment is defined and simulated with the use of AnyLogic in order to properly define the whole assembly process. The final plant layout is completed with the dimensioning of other main facilities and areas useful to support the assembly process.