Rates of homogeneous nucleation of H₂O droplets in a temperature range from 236.37 to 237.91 K and of D₂O droplets from 241.34 to 242.33 K were measured. The single microdroplets consisted of pure H ₂O or D₂O and were levitated in an electrodynamic balance. In comparison to H₂O, D₂O shows a stronger tendency to nucleate. Over the investigated temperature interval, D₂O droplets need to be supercooled less by 1.1 K compared to H₂O droplets in order to arrive at the same nucleation rate. This is in good agreement with the higher degree of intermolecular association in liquid D₂O, a fact which has been well established previously both from theory and experimental studies.