Titan, Saturn's largest satellite, maintains an atmosphere composed primarily of nitrogen (N 2 ) and methane (CH 4 ) that creates complex chemistry. Within this complex chemistry exist nitrile (or cyanide) molecules that have a -CN group. These molecules are known to have substantially enhanced 15 N abundances compared to Earth and Titan's dominant nitrogen (N 2 ) reservoir. The 14 N/ 15 N isotopic ratio in Titan's nitriles can provide better constraints on the synthesis of nitrogenbearing organics in planetary atmospheres as well as the origin of Titan's large nitrogen abundance. Using high signal-to-noise, disk-integrated observations obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 receiver (211-275 GHz), we determine the 14 N/ 15 N and 12 C/ 13 C isotopic ratios of acetonitrile (CH 3 CN) in Titan's stratosphere. Using the Nonlinear optimal Estimator for MultivariatE spectral analySIS (NEMESIS), we derived the CH 3 CN/ 13 CH 3 CN ratio to be 89.2 ± 7.0 and the CH 3 CN/CH 3 13 CN ratio to be 91.2 ± 6.0, in agreement with the 12 C/ 13 C ratio in Titan's methane, and other Solar System materials. We found the 14 N/ 15 N isotopic ratio to be 68.9 ± 4.2, consistent with previously derived values for HCN and HC 3 N, demonstrating an enhanced 15 N abundance in Titan's nitriles compared with the bulk atmospheric N 2 value of 14 N/ 15 N = 168 suggesting a significant role of fractionation in Titan's nitrogen chemistry.