Introduction COVID-19 is known to induce plasma cell differentiation by elevating interleukin-6 level. Proliferation of dyscrasic plasma cells lead to production of monoclonal immunoglobulins. Cases with monoclonal gammopathy in COVID-19 have been reported in various countries. In this study, we present nine cases of Korean patients diagnosed with COVID-19 infection, and their consecutive electrophoresis results of monoclonal gammopathies. Material & Methods A total of 34 serial serum samples from 9 patients diagnosed with COVID-19 infection were analyzed for the protein electrophoresis, immunofixation, immunoglobulin quantification, SARS-CoV-2 antibody titers and interleukin-6 level assessments. Cases were classified into four groups based on the disease severity. Results Six cases revealed the presence of monoclonal paraprotein in serum electrophoresis results. Both two expired cases showed monoclonal bands, with one case of notable correlation with the increase of virus activity. Types of immunoglobulins were variable among six cases. Most of the cases showed high interleukin-6 levels and COVID-19 antibody titers, but their fluctuations did not correlate with monoclonal paraprotein patterns. Conclusions In conclusion, monoclonal paraproteins were observed with relatively higher frequency in the severe cases rather than mild cases. Longitudinal monitoring on monoclonal paraproteins associated with COVID-19 infection were proved to be transient in mild cases.