A 1000-km scale three-dimensional (3D) acoustic tomography experiment has been conducted in the Kuroshio Extension region from July to September 1997. The 3D temperature fields show the energetic meander of the Kuroshio Extension with high time resolution. Mesoscale eddies associated with the meander with horizontal scale greater than 200-km are resolved in the tomographic inversion. These results are consistent with other measurements such as ADCP, XCTD and TOPEX/POSEIDON satellite altimetry. Variable oceanic structures in a 1000-km domain, which are difficult targets for conventional point measurement techniques, can be measured well by ocean acoustic tomography with real-time data telemetry. ¿ 1999 American Geophysical Union