Cr-doped CuO nanostructures have been synthesized via a one-step hydrothermal approach. Field emission scanning electron microscopy results exhibit the morphology evolves from the sheet-like to rod-like structures with increasing Cr doping. X-ray diffraction results demonstrate the variation in preferred orientation and the lattice distortion induced by copper vacancies (V-Cu). The analyses of Raman and PL spectra also prove the structure defects exist in the synthesized samples. The room temperature ferromagnetism (RTFM) was discovered in this system. This literature firstly studies the magnetic property in Cr-doped CuO system and reasonably reveals the desired FM originating from the V-Cu defects.