As more emphasis is placed on renewable energy worldwide, the electrochemical splitting of water has attracted considerable attention. Herein, a simple and cost-effective electrocatalyst was studied for both the hydrogen and oxygen evolution reactions. The electrocatalyst consisted of an electrodeposited cobalt diselenide/cobalt oxide composite, which was fabricated from an aqueous solution containing cobalt and selenium salts on a glassy carbon substrate. The optimal deposition conditions were found to be a fixed potential at −1.2 V vs Ag/AgCl for 400 s. At this relatively low potential, the electrodeposition process is accompanied by the hydrogen evolution reaction, resulting in a hierarchical, flower-like morphology. The electrochemical active surface area was calculated to be 89 cm2 in 1.0 M KOH and 72 cm2 in 0.5 M H2SO4. This electrocatalyst facilitated the hydrogen evolution reaction in both KOH and H2SO4 solutions, with overpotentials of 305 and 205 mV at 10 mA cm–2, respectively. Similarly, good oxygen evolution activity was achieved in KOH. The electrocatalyst demonstrated good stability over a 24 h period, with evidence of improved oxygen evolution activity following the stability studies.