The total cross-section of beryllium oxide for cold neutrons of mean wavelength 5.55 Å has been measured in the temperature range from 100 to 1000°K. The results are satisfactorily interpreted in terms of the incoherent approximation using the Placzek expansion. The values of the Debye temperature obtained from these measurements in the low and high temperature ranges are compared with those got by specific heat measurements. A method of choosing the effective mass and effective neutron cross-section of a molecule in a diatomic lattice is suggested.