The exposure of Taiheiyo and Blair Athol coal chars to air at ambient temperature led to the adsorption of an appreciable amount of N-2 on the coal chars. Some of N-2 thus adsorbed still remained on the chars even after purging the chars with He gas flow. The amount of remaining N-2 was determined by the subsequent temperature-programmed desorption experiment, and it was found that the remaining N-2 accounted for a substantial portion of nitrogen content determined by ultimate analysis using an instrumental analyzer for each coal char. In other words, the amount of nitrogen determined by an instrumental analyzer is overestimated. Accordingly, to obtain the correct nitrogen analysis value, it is necessary to remove such adsorbed N-2. Evacuation of coal chars at 423 K for 5 h prior to the analysis is enough for this purpose.