We recorded the rotational spectra of N-2-ethylene sulfide (ES) and N-2-dimethyl sulfide (DMS) including the N-15(2) and (NN)-N-15-N-14 isotopomers in the frequency range of 5-25 GHz by using a Fourier transform microwave spectrometer. The b-type transitions for the ortho and para states of N-14(2)-ES and N-15(2)-ES and c-type transitions of N-14(2)-DMS and N-15(2)-DMS were observed. The (NN)-N-15-N-14-ES and (NN)-N-15-N-14-DMS species were found to exist in two isomeric forms: inner ((NN)-N-14-N-15-ES and (NN)-N-14-N-15-DMS) and outer ((NN)-N-15-N-14-ES and (NN)-N-15-N-14-DMS). Neither the -ES nor -DMS complexes showed weak accompanying spectra, which had been observed for N-2-ethylene oxide (EO). This is because the potential barriers to internal rotation of ES and DMS are higher than that of EO. The spectra were analyzed by an A-reduced asymmetric-top rotational program with less than 4 kHz standard deviation, except for the (NN)-N-15-N-14-DMS and (NN)-N-14-N-15-DMS complexes. Rotational, centrifugal distortion, and nuclear electric quadrupole coupling constants were determined by the spectral analysis. The V-3 potential barrier to internal rotation of the two equivalent methyl groups of DMS in the ortho and para states of the N-15(2)-DMS complex was determined to be about 740 cm(-1). We performed ab initio calculations in order to complement the information on the intracomplex motions obtained from the experimental spectra