A cable block-locking mechanism of a dual mode shift lever unit having a shift lever pivotally connected to a pivot shaft in a lever housing via a lever bracket provided at a lower end of the shift lever, a rotation member rotationally mounted on the pivot shaft, and a cable block pivotally mounted on the pivot shaft outside the lever housing. The cable block-locking mechanism includes a stud slidably mounted to the cable block for selectively connecting the cable block with the lever housing, a push rod formed on the lever bracket for depressing the stud so as to release the cable block from the lever housing in an automatic mode, and a return spring mounted around the stud for returning the stud to its place so as to couple the cable block with the lever housing in a manual mode.