A process for stabilization of biological sludge provides the step of laying in a containing volume, or basin (1), a draining material (2). In particular, the layer of draining material (2) can be a layer of gravel having granulometry set between 40 and 70 mm and a height (hi) about 25 cm. On the first layer (2) a second draining layer (3) can be laid comprising a material, for example gravel having granulometry less than the first layer (2), set between 4 and 6 mm. The second layer (3) has preferably a height (h2) about 15 cm. Once made the draining layers (2, 3) a planting step is made in the second layer (3) of a plurality of seedlings of an aquatic macrophyte, preferably Phragmites australis (10). The base granular filtering gravel layer has also the function of supporting the root of the seedlings. To ensure a high efficiency of the process a measured density of plants is chosen, corresponding to a relative distance between two seedlings of Phragmites australis set between 40 and 60 cm. once achieved a measured vegetative growth, a first spilling in the containing volume (1) is carried out of an amount of biological sludge (12). The amount of sludge (12) fed in the containing volume (1) corresponds to a predetermined height, set between 2 and 4 cm, of the layer of sludge (12) on the draining layer (3).