Monitoring and evaluation of critical quality attributes (cQA) in monoclonal antibodies (mAb) are a regulatory requirement in pharmaceutical industry. High molecular weight (HMW) species are of critical importance due to the potential risk associated with immunogenicity. HMW species are typically monitored by size exclusion chromatography (SEC). Although low molecular weight (LMW) species are also detected by SEC, low-resolution separation of LMW limits its capability to monitor mAb fragmentation. Recently, we have developed new methods for LMW characterization and evaluation based on the Wes instrument from ProteinSimple. The capillary western blot is based upon size-based separation in a capillary system, and detection by specific immunoprobing, following the separation. The capability of this method for characterization of mAb fragments were demonstrated. The characterization was achieved by probing two antibodies targeted to specific regions (Fc region or Fab region) of IgG1 protein. The specificity of these two antibodies was evaluated against F (ab’) 2 and Fc/2 fragments generated from Ides enzyme treated IgG1 protein. The results showed the selected antibodies provide high specificity to F (ab’) 2 and Fc/2 fragments. Fractions collected from SEC were used to evaluate this method. The detected fragments from SEC fractions were identified based on their estimated molecular weight and antibody detection. The result proved the capability of the capillary western blot as a characterization method for IgG1 fragments. In addition, with the specific detection to IgG1 and IgG4, the power of the capillary western blot to specifically characterize and evaluate individual IgG fragmentations in an IgG1 and IgG4 mixture was also demonstrated. When heat stressed samples were used, results showed method capability as stability indicating in IgG1 and IgG4 mixture samples. The stressed mixture samples were also evaluated by the total protein assay in which protein samples were biotinylated after separation and were labeled with HRP linked streptavidin to provide chemiluminescence detection. The results indicated total protein assay can be a useful complementary method to capillary western blot immunoassay.