The design of efficient bifunctional electrocatalysts for overall water splitting is an essential task for the production of hydrogen. Co3O4 has been developed as highly efficient OER electrocatalysts but with almost no activity for HER. The formation of oxygen vacancies in Co3O4 could significantly enhance the OER and HER activity, Mn-doping are relatively infrequent in this field. In this work, Co3O4 is modified by doping Mn to introduced oxygen vacancies for high-efficiency water splitting performance. The Mn doped Co3O4 shows excellent performance towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with a low overpotential at 10 mA·cm−2 of 157 mV and 265 mV, and an applied potential of 1.54 V at 10 mA·cm−2. The excellent electrocatalytic performance is mainly attributed to oxygen vacancies in Co3O4, rational adjustment of the electronic structure of active sites to increase the intrinsic activity of Co3O4. The Mn doped Co3O4 can be a promising bifunctional electrocatalyst for overall water splitting.