Alkali-retting was applied to kenaf bast ribbons and the mechanical properties and the structure of the retted fibers were investigated. In order to produce the fibers with preferable surface smoothness, the retting should be made at the NaOH concentration higher than 4 %. The tensile properties, however, showed a maximum at the NaOH concentration of 1 %, and decreased with increasing NaOH concentration. It seems difficult to prepare the fibers with preferable surface smoothness without loosing tensile strength only through the alkali-retting.