A spherical carbon material of meso-carbon microbead (MCMB) was examined as an anode in a polyethylene oxide (PEO) based polymer electrolyte lithium battery. The electrochemical performance of the carbon electrode with the polymer electrolyte depended on the electrode thickness and the particle size of MCMB. The 30μm-thick electrode of MCMB with the particle size of 20–30μm showed a reversible capacity comparable with that in a liquid electrolyte, but the 100μm-thick electrode showed a half of the 30μm-thick electrode. The smaller particle size of 5–8μm exhibited a high irreversible capacity at the first charge–discharge cycle. The reaction heat between MCMB and the polymer electrolyte was 0.5JmAh−1, which was much lower compared to those between lithium metal and the polymer electrolyte, 1.2JmAh−1, and MCMB and conventional liquid electrolyte, 4.3JmAh−1.