The nitriles present in the atmosphere of Titan can be expected to exhibit different N-14/N-15 values depending on their production processes, primarily because of the various N-2 dissociation processes induced by different sources such as ultraviolet radiation, magnetospheric electrons, and Galactic cosmic rays. For CH3CN, one photochemical model predicted a N-14/N-15 value of 120-130 in the lower stratosphere. This is much higher than that for HCN and HC3N, similar to 67-94. By analyzing archival data obtained by the Atacama Large Millimeter/submillimeter Array, we successfully detected submillimeter rotational transitions of (CH3CN)-N-15 (J = 19-18) located in the 338 GHz band in Titan's atmospheric spectra. By comparing those observations with the simultaneously observed CH3CN (J = 19-18) lines in the 349 GHz band, which probe from 160 to similar to 400 km altitude, we then derived N-14/N-15 in CH3CN as 125(-44)(+145) . Although the range of the derived value shows insufficient accuracy due to limitations on data quality, the best-fit value suggests that N-14/N-15 for CH3CN is higher than values that have previously been observed and theoretically predicted for HCN and HC3N. This may be explained by the different N-2 dissociation sources according to altitude, as suggested by a recent photochemical model.