An organic radical polymer (ORP) was prepared by radical polymerization and following oxidation into nitroxyl radical. Two different oxidation methods were employed and their radical concentrations were measured using electroparamagnetic resonance spectroscopy (EPR) and UV-visible absorption (UV-vis) spectroscopy. From these measurements, _ xml_ns="http://www.w3.org/2000/svg" class="gs_fsvg" aria-label=" H_2O_2-Na_2WO_4 " width="111px" height="12px" style="color: rgb(34, 34, 34); font-family: Arial, sans-serif; font-size: 13px; font-variant-numeric: normal; font-variant-east-asian: normal; vertical-align: -2px;"> oxidation method exhibited a complete oxidation, which resulted in 97.6% spin concentration. Also, it was revealed that convenient and cheap UV-vis measurement was useful for preliminary radical concentration comparison. After applied as a cathode material in lithium ion batteries, ORP electrode showed a high initial capacity (_ xml_ns="http://www.w3.org/2000/svg" class="gs_fsvg" aria-label="110 mAh\; g^{-1} " width="77px" height="14px" style="color: rgb(34, 34, 34); font-family: Arial, sans-serif; font-size: 13px; font-variant-numeric: normal; font-variant-east-asian: normal; vertical-align: -3px;">), a good initial efficiency (96%), a very high rate performance (70% charging during 1.2 min) and stable cycle performance.​