The research was conducted in the area of Croatian Posavina, in the floodplain belt of the river Sava. The structural features, and economic and non-market values of narrow-leaved ash stands in relation to site conditions were analysed. In terms of principal tree species, the sites in Posavina can be divided into oak and ash sites. The differentiation between these, and especially the transitional ones, is of primary importance for forestry, as management goals and methods, particularly the method of regeneration, depend on the properties of the sites. Narrow-leaved ash grows in three groups of sites called wet micro-depressions, unsoaked micro-depressions and micro-elevations, with characteristic soils consisting of amphigleys, hypogleys and semigleys. The local names of these sites (bara, niza and greda), in fact reflect the water regime and the micro-relief with minimal relative height differences of occasionally only 10 cm. Narrow-leaved ash grows successfully in all the above-mentioned sites, but forms pure ash stands only in wet micro-depressions. The changing micro-relief in micro-depressions cause stands to have different properties. So, there are wet, humid and dry types of pure narrow-leaved ash stands in a micro-depression. In an unsoaked micro-depression, narrow-leaved ash grows in mixed stands with pedunculate oak. On a micro-elevation, it is mixed with pedunculate oak and common hornbeam. The least favourable site conditions for the growth of forest trees are found in wet micro-depressions, slightly better ones are in unsoaked micro-depressions, while the most favourable ones exist on micro-elevations. Due to its ecological characteristics and biological properties, narrow-leaved ash is capable of tolerating various sites. As highly unfavourable swampy conditions can be tolerated only by narrow-leaved ash, this is the reason why wet micro-depressions are inhabited by pure ash stands. In other sites, more favourable conditions allow the growth of other tree species, in particular of pedunculate oak, which results in the establishment of mixed stands. Stands of narrow-leaved ash growing in wet micro-depressions have very low economic value compared to other stands in which it occurs. However, their ecological and social value is high.