We present observations of isotopic lines of dense gas tracers toward the nuclear region of nearby Seyfert 2 galaxy NGC?1068 with the IRAM 30 m telescope and the Atacama Pathfinder Experiment (APEX) 12 m telescope. We detected four isotopic lines (H13CN 1-0, H13CO+ 1-0, HN13C 1-0, and HC18O+ 1-0) at the 3 mm band with the IRAM 30 m telescope and obtained upper limits of other lines. We calculated optical depths of dense gas tracers with the detected isotopic lines of HCN 1-0, HCO+ 1-0, and HNC 1-0. We find that the 14N/15N abundance ratio is greater than 420 if we adopt the upper limit of HC15N(1-0) emission. Combining this with fluxes of 1-0 lines from IRAM 30 m observations and the upper limit of 3-2 lines from APEX 12 m observations, we also estimated the excitation condition of molecular gas in the nuclear region of NGC?1068, which is less dense than that in the extreme starburst regions of galaxies.
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