Plant fibers have recently been widely used in the construction sector due to their mechanical properties, biodegradability, and low environmental impact. As environmentally ecological materials, natural fibers used as reinforcement for cementitious materials are an alternative to synthetic fibers. According to various literature research, adding fibers can improve workability, strength, and concrete durability. Natural fibers can also lead to an improvement in the thermal and acoustic characteristics of the resulting concrete. This experimental research examines the mechanical performance (flexural strength) of cementitious mortars reinforced with hemp fabric fibers (non-treated or alkali-treated). The hemp fiber fabrics treatment is performed with a 5% NaOH solution to improve the fiber-matrix interface and its mechanical properties. Three-point bending tests were performed on mortar prismatic specimens reinforced with a layer of hemp fiber fabric added at different positions. The results show that using non-treated hemp fiber fabric as reinforcement in mortar improves mechanical resistance by an increase of over 40% in ultimate load on the flexural strength. Furthermore, reinforcement with alkali-treated hemp fiber fabric shows an increase of over 70% in the flexural strength of specimens compared with the specimens of reference. The obtained results encourage further research on hemp fiber fabrics as a reinforcing element in mortar.