The concept of ecological function, here presented, is the result of epistemological endeavours on the city and its functions. We consider that the city, which has the features and the properties of a living organism”, must not be assessed and analyzed from a Cartesian point of view, but functionalistically. The definition that we propose for the city, is that of an organized and complex geographic space, with a permanent dynamic, capable of ensuring a diversity of functions for its evolution and development, as well as for the evolution and development of its influence space. This definition is based on an entirely different axiology and its underlying concept is finality. The city’s finality generates a new definition of the urban function, which is the relationship of necessity formed between the elements of the urban geosystem and its state and which generates, cultivates and sustains the city`s life, working towards the attainment of its systemic finality. The two concepts, defined through a new philosophy, offer us a new perspective on the classification of urban functions, in which, objectively, the category of civic-urban functions sets in, containing among others the ecological function. This function has never been classified or even mentioned in the geographic literature. Having based our endeavour on the General System Theory and on the fractal theory, we considered the ecological function`s subsystem as a geosystem with all the necessary defining features, and we built an analysis, diagnosis and prognosis scheme for the subsystem of the ecological function of Cluj-Napoca.