This volume of Advances in Soft Computing and Lecture Notes in Computer Science vols. 5551, 5552 and 5553, constitute the Proceedings of the 6th International Symposium of Neural Networks (ISNN 2009) held in Wuhan, China during May 26 - 29, 2009. ISNN is a prestigious annual symposium on neural networks with past events held in Dalian (2004), Chongqing (2005), Chengdu (2006), Nanjing (2007) and Beijing (2008). Over the past few years, ISNN has matured into a well-established series of international conference on neural networks and their applications to other fields. Following this tradition, ISNN 2009 provided an academic forum for the participants to disseminate their new research findings and discuss emerging areas of research. Also, it created a stimulating environment for the participants to interact and exchange information on future research challenges and opportunities of neural networks and their applications.