Based on capillary zone electrophoresis (CZE), we validated a method of confirming the identity and purity of the separated charge variants of monoclonal antibodies (mAbs) and antibody-drug conjugates (ADCs). The validation includes the evaluation of the specificity, linearity, quantitation limit, precision (repeatability and intermediate precision), accuracy, range, and robustness. The method is applicable to the majority of mAbs and ADCs (with pI from 7 to 9 and a drug to antibody ratio up to 8), requiring no modification to the method conditions. The proposed CZE method showed reproducible separation profiles, while cation exchange chromatography (CEX) showed low reproducibility and deficient separation profiles due to an undesirable interaction between the separation column and the low molecular weight drugs combined in the ADCs. Since CZE is able to minimize this undesirable interaction during the separation, it proved to be a useful separation methodology for evaluating charge variants of ADCs. The validation of CZE for assessing ADCs was successfully demonstrated for the first time, and show that CZE is suitable for the separation method for detecting the charge heterogeneity of ADCs.