Cr0.046Zn0.954O nanowires (NWs) were synthesized by electrospinning and treated with different atmosphere (O-2 and H-2) annealings. Our work demonstrates that not all the oxygen vacancies can really contribute to the ferromagnetism of cationic Cr3+-doped ZnO (Cr0.046Zn0.954O) electrospun NWs. The photoluminescence measurements show that the single positively charged oxygen vacancy (i.e., V-o(+) or F+ centers (F-c)) bound defect states are quite stable in Cr0.046Zn0.954O NWs. Upon hydrogen-annealing, the specifically deep-level defect F-c was annihilated; thus, an electron transfer may occur from shallow donor H+ (e(-)) to deep donor F-c. An electron paramagnetic resonance signal at g similar to 2.0583 was found in the Cr0.046Zn0.954O NWs, which is responsible for Cr3+ -F-c complex formation, and a weak broad signal at g similar to 15.5807 is considered as another paramagnetic center of Cr-Cr impurity pairs generated in the H-2-annealed Cr0.046Zn0.954O NWs. The hydrogen-annealing offers an easier way to F-c engineering where a precise control of magnetic properties of diluted magnetic semiconducting oxide NWs is sought. Published by AIP Publishing.