We revealed many coincidencies of generation lines frequenciesof FIR lasers and absorption lines frequencies of strong lines ofthe rotational spectrum of formic acid molecule. The results arereported in Table 1. We used FIR lasers frequencies which have beenreported in N.G.Douglas handbook MA. And absorption linesfrequencies of fomic acid have been obtained when we investigatedthe rotational spectrum of these molecules in frequency range up to400 GHz. About 8,000 frequencies of absorption lines of HCOOH,DCOOH, H000D, DCOOD, H13000H, D13000H, H13000D, D13000D, HC1800H,HC0180H, DC1800H, DC0180H, DC1800D, DC01801) in ground state and,part icully, in exited vibrational ones were measured. Accuracy ofthese measurements was Ã‚Â± 20 50 kHz. As a result the sets of rota- tional and centrifugal molecular parameters of Watson's Hamilto- nian, 0 representation, have been obtained for each species.