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The present work reports an enhancement in the electrochemical properties of Li2RuO3 by Co+3 substitution. We explore the Li1.33‐x/3Ru0.66‐2x/3CoxO2 series (in the solid solution notation (x)LiCoO2‐(1‐x)Li2RuO3) for x≤0.4 by partial substitution of Co+3 for both Ru+4 and Li+ in the metal layer; in this way, creation of oxygen non‐stoichiometry is avoided. Powder XRD reveals that an increase in the cobalt content in the series leads to a structural transformation from monoclinic to rhombohedral phase, owing to increased cation disorder in the metal layer. Cyclic voltammetric scans shows clear evidence for decreased oxygen evolution for Co‐substituted samples. The x=0.3 member delivers an initial discharge capacity of about 232 mAh g−1 and, after the 100th cycle, 85 % capacity retention is observed. Furthermore, the rate capability is also significantly improved by Co substitution. Li+ removal during the first charge is more than expected by counting on cation oxidation alone, demonstrating the participation of anion redox. Interestingly, the x=0.2 and 0.3 members of the series Li1.33‐x/3Ru0.66‐2x/3CoxO2 show better Li reversibility upon long‐term cycling, endorsing the beneficial effect of Co+3 in stabilizing the layered structure during electrochemical cycling.