Synthesis and CO2 absorption properties of single-phase Li2CuO2 oxide were studied by X-ray powder diffraction and thermogravimetry. Samples of Li2CuO2 were prepared in solid state using Li2CO3 and CuO as starting reagents. A mixture of Li2CO3 and CuO was heated at temperatures of 600-1000 degrees C and then quenched to room temperature. From XRD, it was found that single-phase Li2CuO2, can be obtained by heat treatment at 680-685 degrees C with the quenching operation. The single phase was never obtained without quenching; that is, quenching rate (degrees C s(-1)) seems to be an important factor which determinates whether sample is obtained as a single phase or not. From thermogravimetry, it was found that Li2CuO2 begins to absorb CO2 at around 230 degrees C, then drastically absorbs CO2 at over 600 degrees C, reaching 40.2 mass % maximum CO2 absorption, and finally emits CO2 over 900 degrees C. The maximum CO2 absorption (40.2 mass %) is larger than that (36.7 mass %) of Li4SiO4 CO2 absorbent.