Electrochemically active oxides play important roles in the fabrication of electrochemical sensing platforms, in which they can be utilized as electrochemical probes or catalysts in electrochemical reactions. Herein, a novel ratiometric electrochemical sensor for uric acid (UA) was developed based on the newly synthesized Cu₂O nanocubes with good electrochemical activity combined with boron carbide (B₄C) with excellent conductivity. The oxidation peak of Cu₂O remained unchanged, which could be used as a reference, while the oxidation peak of UA catalyzed by the modified electrode increased with the concentration of UA. The two signals displayed a large peak-to-peak potential and thus a ratiometric electrochemical sensor for UA was established, which could further reduce the effects of unrelated factors, such as the environment influence. The sensor exhibited good linear ranges of 0.1–100 μM and 100–1000 μM, and showed good sensitivity, selectivity, repeatability, and stability. The sensor was successfully applied in the detection of UA in complex human serum and urine samples.