In Daloa, Côte d’Ivoire, many coffee and cocoa plantations that have fallen into decline and been left fallow are being reused. In order to prevent the failure of the planned crops, this study aims to determine the biological functioning of these soils, which is essential for developing sustainable management strategies for them. Seven fallows older than ten years were identified. In each of them, a plot of 10,000 m2 was delimited and four monoliths were isolated. Each monolith was sorted in order to extract the organisms, identify them and calculate their density. A soil sample was also taken from each stratum for analysis. The biological functioning of the soil was determined by considering that the density of fauna is an indicator variable of the biological fertility of the soil, which is then correlated with CEC and texture, two variables considered to explain soil fertility in general. The results show that the density of the macrofauna constituting the soil engineers varies little on the sites, maintaining a relationship with either the sand or silt content of the soil, or with the CEC of the soil, or both variables. Soils where the CEC has been improved by the action of fauna are likely to function better and the types of fauna involved have been identified as the main biological actors in the fertilisation of the soils studied.