Calculation of magnetic susceptibility for the different valence bond structures indicate that ozone should be diamagnetic, the susceptibility being about −18×10⁻⁶ while reported experimental values show that it is feebly paramagnetic in the liquid state, diamagnetic values being reported for the gaseous state. The possible causes of the discrepancy and a comparison with oxygen are discussed. The magnetic behaviour may be considered to conform to what may be expected from other physical properties of ozone.