© 2020 The Obesity Society. Objective: This study aimed to determine whether higher membrane capacitance (CM), a bioelectrical measure of cell membrane function, is associated with insulin resistance (IR) and/or metabolic syndrome (MetS). Methods: Cross-sectional analyses were performed on 2,191 relatively healthy adults from the National Health and Nutrition Examination Survey. The CM of those with low/no disease risk was compared with those with IR, MetS, or both IR and MetS using ANCOVA. The associations between CM and related clinical measures were assessed with multiple linear regression. Results: Compared with those with low/no risk, women and men with IR (P < 0.001) and IR + MetS (P < 0.001) had higher CM, whereas CM was similar in women (P = 0.4526) and men (P = 0.1126) with MetS alone. Positive associations with CM were seen with waist circumference (women and men standardized beta [STD-β] = 0.18, P < 0.0001) and fasting insulin (women STD-β = 0.15, P < 0.0001; men STD-β = 0.12, P < 0.0001). Conclusions: Higher CM was associated with IR in relatively healthy adults. In the absence of IR, higher CM was not associated with MetS as defined by its clinical diagnostic criteria. This study suggests that with further investigation, CM may be a potential tool to detect IR-related cell membrane dysfunction.