Frequency and voltage dependent electrical characteristics are reported for Ni/ZnO Schottky diodes. Schottky diodes are realized from nano-structured ZnO thin films grown by DC magnetron sputtering. Electrical characterizations are performed by current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements. The diode parameters are extracted, such as barrier height (phi(B)), ideality factor (n) and carrier concentration (N-D). The diodes exhibited a non-linear rectifying behaviour with a barrier height of 0.68 eV and an ideality factor greater than unity. Charge transport mechanism and possible reasons responsible for non-idealities are investigated. The density of interface states (N-SS) below the conduction band are extracted from the measured values of I-V and C-V as a function of E-C - E-SS. From E-C- 0.51 to E-C - 0.64 eV below the conduction band edge, the interface state density N-SS is found to be in the range 1.74 x 10(12)-1.87 x 10(11) eV cm. The interface states density obtained from capacitance-frequency (C-f) characteristics varied from 0.53 x 10(12)-0.12 x 10(12) eV cm from E-C 0.82 eV to E-C 0.89 eV below the conduction band. A complete description of current transport and interface properties is important for the realization of good quality Schottky diodes and for the design and implementation of high performance electronic circuits and systems.