Abstract: Geotechnical engineering requires the use of ecologically acceptable, long-lasting, and effective solutions to fortify clayey soil. The mechanical behavior of clayey soil strengthened with carbon fibres (CFs) was studied in this work. Soil specimens were subjected to uniaxial compression strength tests at their optimal moisture content (OMC). The impacts of CFs length and percentage on the strengthened soil specimens' shear resistance, and stress-strain curve behavior were investigated. The effect of CFs on specimen cohesiveness and angles of internal friction was also investigated. The results showed that adding CFs to clayey soil can increase its shear resistance and cohesiveness greatly. Because the fibres can be spread easily in soil samples and had a suitable length that can generate an interlaced network among soil grains that restricted soil movement once exposed to external stresses, it is presumed that utilizing three percent of CFs weight content had six millimeters length could indeed give the highest impact on resistance development among all the specimens.