Although abnormalities of glycosylation profile in serum IgG have been demonstrated in a variety of inflammatory autoimmune diseases such as rheumatoid arthritis, there are only a few reports describing long term monitoring of N-glycosylation profiles in such patients. Here we report the serial finding of N-glycosylation profiles of IgG-kappa M-protein in a patient with multiple myeloma monitored for two years. In this patient, serum formed a gel precipitation upon exposure to air. The HPLC mapping method demonstrated that IgG M-protein in the patient exhibited a significant decrease in the ratio of fucosyl to afucosyl N-glycans compared with that in a healthy control. With remission, the IgG M-protein showed an increase in this ratio, becoming closer to that in the healthy control. However, the gel-precipitation persisted. This finding suggested that this unique property of serum may not be related to the glycosylation profile of the M-protein.