The hydrothermal approach was adopted for the fabrication of zinc oxide (ZnO) nanofibers. The effect of hydrothermal reaction time (1–20 h) was studied on the basis of dielectric, structural, morphological and optical properties. The techniques, i.e., X-ray diffraction (XRD), Fourier transform infrared microscopy (FTIR) and energy dispersive spectrum (EDS) were employed for the characterization of ZnO nanofibers (NFs) formation. In XRD studies, reflection planes (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0) and (1 0 3) are well matched with wurtzite ZnO hexagonal structure. The presence of ZnO NFs at 20 h of reaction time can be attributed that intensity along (0 0 2) plane becomes stronger or preferential growth on 1D. Structural defects were calculated by employing the dislocation density. The grain size of ZnO NFs was in 18.4–29.7 nm range. The absorption peak at 605 cm−1 (at higher reaction temperature) confirms the formation of 1D nanostructure. SEM analysis reveals the ZnO NFs formation at higher hydrothermal reaction time and EDS confirms the purity of ZnO samples (77.67% of Zn and 22.33% of O). The optical properties found to be also affected as a function of hydrothermal reaction time. Findings revealed that the ZnO can be fabricated by hydrothermal treatment to enhance the dielectric, structural and optical properties for photocatalytic application.