Vertisols in Northern Tunisia are fertile, stable, black, and rich in clays. They are located in a sub-humid bioclimatic region. However, they have been poorly studied, despite their environmental and economic importance. The main objective of this study is to investigate the impact of Vertisols clay on the organic matter and moisture content of the vertic soil of Beja (Northern Tunisia). This region possesses the ideal type of Vertisols in Tunisia, which exhibit high productivity for annual crops. Fifteen soil samples were collected from three soil profiles along a toposequence spanning 500 meters, from top to the bottom of slope. In these Vertisols, where horizons were absent in the profiles, samples were taken from five layers (systematic cut), each 20 cm thick, reaching a depth of one meter. The sampling was conducted at the end of the summer. Physico-chemical analysis revealed a significant clay fraction, around 70%, in the deepest layer. X-ray diffraction shows that this fraction is dominated with illite and kaolinite. The results exhibited slight homogeneity, even with the influence of the slope, and confirm the leaching effect of clays on Vertisols. The percentage of illitic clay increased with depth from 55.2% (0–20 cm) to 61.9% (80–100 cm). Whereas, for example, in the mid-slope profile, organic matter decreased from 4.4% (0–20 cm) to 2.9% (80–100 cm), while, the highest moisture content was recorded in the deeper layers: 12% (0–20 cm) and 35% (80–100 cm). Thus, the compaction and shrinkage-swelling of clays explained the variation of the humidity values. The presence of such clays with a minimum content of 48.7% with a significant amount of organic matter and moisture content, ensures chemical fertility and promotes good crop growth.