The absorption cross-section of ozone at 253.7 nm is frequently used as a standard for the entire UV wavelength range. The presently accepted value is 1.147¿10-17 cm2, known with an uncertainty of about 2%. The cross-section has been recently measured by simultaneously monitoring the ozone pressure, the impurities in the ozone gas, the gas temperature and the UV beam intensity. The cross-section at room temperature was found to be 1.137¿10-17 cm2, having an uncertainty of ¿.7%. The improved accuracy will aid a number of ozone experiments including the in situ photometers and Solar Backscatter Ultraviolet instruments.