The microwave spectra of gaseous 1-fluoronaphthalene and 2-fluoronaphthalene have been measured using three different Fourier transform microwave spectrometers in the frequency range of 1.8–10GHz, with substantial improvements in resolution over previous measurements. The measurements include 15 a-dipole and 15 b-dipole transitions for 1-fluoronaphthalene and 12 a-dipole and 16 b-dipole transitions for 2-fluoronaphthalene. Analysis of measured lines for 1-fluoronaphthalene has yielded ground state rotational constants of A=1920.581(2) MHz, B=1122.2370(5) MHz, and C=708.4819(3) MHz. Analysis of the 2-fluoronaphthalene spectra has yielded rotational constants of A=2844.761(2) MHz, B=808.1592(8) MHz, and C=629.5032(3) MHz. Calculated (G09) rotational constants are in very good agreement with measured values.