Recently, it has been reported that certain lots of heparin are associated with an acute, rapid onset of serious side effects indicative of allergic reaction, and (1)H NMR is one of the convenience but strong analytical methods to identify a contaminant in heparin. However, an NMR signal from the contaminant in some cases is overlapped with a satellite peak from heparin, leading a misunderstanding of the presence of the contaminant. Here, we show the satellite peak observed close to the NMR signal of the contaminant, and recommend the (13)C decoupling NMR to discriminate the satellite peak from the contaminant.