This study aimed to estimate the relative contributions from genetic and environmental factors to the Wisconsin Card Sorting Test (WCST) performance, a widely used measurement for assessing frontal lobe function. Participants included 350 pairs of twins (257 MZ and 93 DZ) and 47 same-sex sib-pairs, aged 12–16 years, systematically recruited from junior high schools in Taipei. A computerized version of the WCST was administered for each participant and its nine indexes were used for subsequent analysis. Univariate analysis in structural equation modeling was performed for each WCST index using Mx program. The ACE model for each WCST index indicated no significant genetic influence, whereas the shared environmental influence ranged from 30 to 38% for four indexes (Perseverative Errors, Perseverative Responses, Categories Achieved, and Conceptual Level Responses). We concluded that WCST performance might be an indicator more for environmental insult than for genetic influences on frontal lobe function.