A learning city is one that promotes lifelong learning for all, and sustainable development will be achieved by learning through life. This paper focuses on developing a guideline for building lifelong learning cities in Thailand. We first present findings from studying four learning cities in Thailand and abroad that had similar starting points: the need for problem-solving and urban development. They emphasise the use of education as a tool for human development that will lead to sustainable city development. We then present the analysis of the potential of two Thai cities prepared to be learning cities. Our findings show that their learning goals should be set correspondingly with the problems and identity of the city. There should be a working plan, and the mechanisms for driving and evaluation should be clearly defined. Lastly, we discuss how the guideline for developing a learning city in Thailand -- developed from this study -- should be divided into three phases. The guideline also presents the triangle of a lifelong learning city based upon the 4Com principle: community-communication-commitment-combination. The main goal is to promote lifelong learning and sustainable development.