The current study was conducted to compare the level of cognitive functioning in patients with bipolar disorder by utilizing the brand-new version of the Wechsler intelligence scale, K-WAIS-Ⅳ, and to understand their cognitive characteristics by comparing the bipolar patients group and the normal control group(NC). In addition, the purpose of this study was to understand the relation between cognitive functioning and clinical variables including the age of onset, the length of disorder, the number of mood episodes, the number of previous hospitalizations, and the severity of mood symptoms. K-WAIS-Ⅳ was performed for 58 bipolar patients and 300 people from NC for comparison of their Full Scale IQ(FSIQ), 4 index scaled scores, and 10 scaled scores of subtests. Bipolar patients showed significantly lower performance on FSIQ, working memory index(WMI), and processing speed index(PSI) when compared to NC, and, in particular, they showed the lowest performances on PSI. The performances in digit span, arithmetic, symbol search, and coding, the subtests of WMI and PSI were also significantly poor. These results imply cognitive inefficiency in patients with bipolar disorder. However, no significant correlations were observed among the clinical variables and the FSIQ, four indices.