A controlling structure for a unidirectional ratchet wrench contains a driving head of a unidirectional ratchet wrench, and driving head having a receiving cavity and a groove communicating with the receiving cavity. The receiving cavity has a driving member, and the driving member has a toothed portion. The groove has a retaining block received therein, and the retaining block has a plurality of locking teeth so as to engage with the toothed portion. The retaining block has a slot or a tab so as to retain with the elastic member. The elastic member has a fitting segment, a curved section, and an abutting segment, the fitting segment is fitted into the slot or is retained with the tab, the curved section extends outwardly from the fitting segment and becomes curved, and the abutting segment connects with the curved section and abuts against the groove.