The pure rotational spectrum of chlorine nitrate in its v6 = 1 excited vibrational state has been studied. A total of 2901 lines, with Ka extending to 33 in the 35Cl isotopologue and 30 in the 37Cl isotopologue, respectively, have been recorded and assigned. This analysis, along with our recently reported study of the ν5/ν6ν9 dyad and the improved energy levels of ν9 reported in this paper, should make possible accurate simulation of the corresponding ν6 band and its complex hot band structure near 435 cm−1.