The vapor pressure of ozone has been measured at liquid argon temperatures. At the normal boiling point of argon (-185.9¿C) an ozone pressure of 4.05¿10-2 Torr was obtained with an accuracy of ¿1.5%. Increases and decreases in liquid argon temperatures raised and lowered the ozone vapor pressure, respectively. During the vapor pressure measurements the purity of ozone was monitored with a mass spectrometer. The proposed ozone standard will considerably improve the calibration of experiments for atmospheric research, the determination of absorption cross sections and other labortory ozone studies.