The two lowest vibrational levels of chloroform, HC 35 Cl 3 , v 6 =1 and v 3 =1, have been studied by submillimeter wave spectroscopy in the regions 255–350 and 530–635GHz, corresponding to the ranges of J=38–53 and 80–96. The v 6 =1 level has an accidentally small value of (C−B−Cζ)∼−0.0029cm −1 , which lies in the origin of a global q 22 resonance (Δk=±2, Δl=±2). As a consequence of this resonance, the levels of the v 6 =1 vibrational state exhibit several resonant crossings due to the q 12 l-type interaction (Δk=±1, Δl=∓2), which induce measurable perturbation-allowed rotational transitions.Analysis of these data enabled an independent determination of the C 6 and Cζ 6 constants, which is not a typical case in purely rotational studies of symmetric top molecules. In the spectra of the v 3 =1 level, the splittings of K=3 transitions have been resolved, making the determination of the h 3 splitting term possible.Altogether there have been measured almost 800 rotational transitions in the v 6 =1 vibrational state and more than 250 transitions in the v 3 =1 vibrational state. These have been reproduced quantitatively with standard deviations of 43 and 32kHz in the v 6 =1 and v 3 =1 levels, respectively, leading to considerable improvement of determination of molecular constants of the studied levels.