The pure rotational spectra of phenyl isocyanate (PhNCO) and phenyl isothiocyanate (PhNCS) were investigated using Fourier transform microwave (FTMW) spectroscopy in the range from 4 to 26 GHz. For each molecule, rotational transitions due to the parent species and nine minor isotopologues including seven 13C, one 15N and one 18O/34S have been observed in natural abundance. The rm(1) geometries were derived from the resulting sets of rotational constants and are consistent with the equilibrium structures (re) from ab initio calculations performed at the MP2/aug-cc-pVTZ level. NBO and Townes-Dailey analyses were conducted to better understand the electronic structure and geometry of each compound. In the case of PhNCS, the nitrogen atom displays more sp-like character resulting in shorter C-N bonds and a larger CNC angle relative to those of PhNCO.