Emission spectra of 10B18O and 11 B18O isotopomers in the 230-330 nm region have been investigated by means of conventional high-resolution spectroscopy.The molecules were produced in a low-pressure arc by discharging 8 Torr of mixture containing argon and oxygen 18 in the ratio of 4:1 and the spectra have been recorded using Ebert-type spectrograph.The boron needed to produce BO has been present in the system as amorphous powder with natural abundance of 10B and 11 B.Rotational analysis of the 0, 0 and 0, 1 bands has been performed and spectroscopic constants have been extracted.The results have allowed first determination of the equilibrium rotational constants Be and De for both isotope species 10B18O and 11B18O in their lower electronic state.Assuming a linear dependence of Be on (v + 1/2), the value of equilibrium distance re in the lower state has been derived.