Kitakyushu, an industrial city of about one million residents located at the northern end of Kyushu Island, Japan, is widely cited as a successful model of a polluted smoke-stack industrial city transforming itself into a livable "environment and technology" metropolis. This paper examines how this transformation was accomplished and under what economic circumstances. It also tries to draw lessons we can learn from this experience. The transition occurred over a period of about five decades, from around 1960 to 2010. We can see three distinct phases of this transition: first, a period to combat pollution in the air and water by applying stricter regulations; second, a period to develop new recycling/reprocessing technologies to create new job opportunities; and third, a period to strengthen R&D capability for the low-carbon innovation to extend a global new technological frontier. This paper argues that the economic value of green urban planning lies in its potential to open up new global business horizon making the city sustainable also in terms of its economic viability.