Small-sized freestanding Co3O4 nanosheets have been successfully synthesized on conductive substrate via a novel and simple electrochemical-based strategy. The as-synthesized sheets have a small size of 30 +/- 10 nm in edge length and about 10 +/- 5 nm in thickness with most sheets lying perpendicular to the substrate. The combined properties of products such as small size, two-dimension shape and freestanding pose could lead to integrative advantages of high surface-to-volume ratio, the maximized exposed surfaces without particles aggregation, strong affinity and good conductivity. As for electrochemical tests, the as-synthesized Co3O4 nanosheets show an improved sensitivity of similar to 0.56 A M-1 cm(-2) with lower detection limit of 1 mu M at concentration range of 0-1.8 mM for H2O2 sensing, and also exhibit good performance for oxygen evolution with low evolution over-potential, high catalytic efficiency and durable stability. (C) 2013 The Electrochemical Society. [DOI: 10.1149/2.016303jes] All rights reserved.