Vertical profiles of ozone concentration in the high latitudes were observed by the Improved Limb Atmospheric Spectrometer (ILAS) aboard the Advanced Earth Observing Satellite (ADEOS) from November 1996 to June 1997. The ozone data obtained by the version 5.20 ILAS retrieval algorithm are compared with those obtained by the version 19 Halogen Occultation Experiment (HALOE), the version 6 Stratospheric Aerosol and Gas Experiment (SAGE) II, and the version 6 Polar Ozone and Aerosol Measurement (POAM) II retrieval algorithms. The ILAS data are also compared with ozone data measured by ozonesondes, instruments on board balloons or an aircraft, and ground-based instruments. The ILAS ozone data generally agree with its correlative data between 11 and 64 km with some exceptions. Quantitatively, the median value of the relative difference (absolute difference divided by its mean value) for these comparisons was within ±10%. Relative differences (18%) exceeding the combined measurement errors were found around 45–55 km altitude from comparisons with the HALOE and SAGE II data in January 1997 in the Southern Hemisphere (SH). Larger relative differences (around 50%) were also found below 15 km from comparisons with the HALOE and POAM II data in November 1996 in the SH, but these absolute differences were 0.10–0.16 ppmv as the median value. The ozone data processed by the version 5.20 were improved compared to the former version 3.10, which is available to the general public. The version 5.20 ozone data can be used for scientific analysis purposes based on the accuracy of the data in comparison with these other instruments.