By its frequency, colorectal cancer (CRC) has become a serious public health problem. BAT25 marker is included in the panel of five markers dedicated to the diagnosis of CCR microsatellite instability. The objective of this study was to evaluate the polymorphism and genetic diversity of the BAT25 marker in CRC cases in Senegal. This prospective study was performed on 22 CRC patients. After DNA extraction, the polymorphism and genetic diversity of BAT25 was determined by PCR and sequencing. The alignment of the sequences was carried out using Bio Edit software. The parameters of the polymorphism and genetic variability were determined using the Dnasp, Mega and the Arelquin programs. The results showed a genetic variability of BAT25. This variability is represented by mutations observed in the tumor tissues. The most frequent mutation was the deletion of a thymine at position 72 (T72d). This deletion was absent in healthy tissues and controls. From this study, it can be concluded that the mutations found in the tumor tissues could have a role in the onset, development and progression of CRC.