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Herein, we reported a well-controlled hydrothermal synthesis of Co3O4 nanowires using CoSO4 as a cobalt precursor and glycerol as a morphological directing agent. Scanning electron microscopy was employed to observe the growth of nanowires. As an important synthetic parameter, reaction time is spanned from 4 to 24 h, which played an important role in the morphology and properties of materials. When the reaction time was 4 h, the resulting Co3O4 nanoparticles assembled into some short nanorods. While increasing the reaction time, the nanorods grew into long nanowires with large aspect ratio, and then attached into bundles when the reaction time was extended up to 24 h. Electrochemical characterization shows that Co3O4 nanowires prepared by hydrothermal reaction for 12 h exhibited the highest catalytic activity for oxygen evolution reaction (OER) among all synthesized nanowires and nanoparticles using the similar method. The enhanced OER activity of the 12 h-prepared Co3O4 nanowires should be attributed to the increased electroactive surface area because observed from the cyclic voltammogram, the 12 h-prepared Co3O4 nanowires possessed the highest surface area among all tested samples. It was also illustrated that there existed a close correlation of the OER catalytic activity with the transition of oxidation state and the density of activity sites of the catalyst exposing to the electrolyte solution during the electrolysis. Though both Co3O4 nanowires and nanoparticles exhibited a considerable loss in OER activity during the stability testing, after polarization for 4 h at 1.7 V (versus a reversible hydrogen electrode), the Co3O4 nanowires still produced the higher catalytic current than that of the Co3O4 nanoparticles showing a slightly higher stability than the particles because of the nanowire structure.