The security of ecosystems (eco-security) in urban areas has become a serious problem in fast economic development and urbanization. Regional eco-security and environmental conditions must be improved, first, by understanding eco-security and making assessments of its current status. Based on remote-sensing TM images of Guangzhou and using GIS methods, an index system for eco-security assessment was developed, an assessment was performed with spatially fuzzy sets, and the temporal and spatial dynamics of regional eco-security were analyzed. The index system and gridded pattern of eco-security revealed that the level of eco-security in Guangzhou has been fairly steady with some variation at different times. Before 1995, eco-security was stable but decreased near 1995, when its level was lowest. Comparing different districts, the level in Guangzhou City was lower than that in its suburb districts and in a serious state. The results of assessment for eco-security based on gridding could be shown spatially and visibly, and were useful for spatial comparison to understand different regional eco-security levels. This achievement with the spatially fuzzy set method was an obvious improvement over results obtained by the author with other assessment methods. In eco-security levels, results were the same, but more characteristics for assessment were included in this method, such as the spatial pattern of eco-security. This work shows that using spatially fuzzy sets for regional eco-security assessment is a reasonable and reliable method.