The rotational spectral lines of the H2NS and D2NS radicals in the (X) over tilde(2)B(1) electronic ground state are observed with a source-modulation microwave spectrometer and a Fourier-transform microwave spectrometer. Molecular constants including hyperfine interaction constants are determined for H2NS and D2NS by a least-squares method. By using the obtained centrifugal distortion constants and inertial defects, the harmonic force field is evaluated, and the frequency of the yq vibrational mode (out of plane) is calculated to be 325 cm(-1). This value is much smaller than that of the related molecule H2CS, indicating a floppy motion along the out-of-plane mode. The zero-point vibrational average structure was determined as follows; r(z)(N-H)=1.000(5) Angstrom, r(z)(N-S)=1.6398(13) Angstrom, and angle(z)(HNH)=118.9(7)degrees, where the numbers in parentheses represent three times the standard deviation.