Overview of Improved Limb Atmospheric Spectrometer (ILAS) instrument design, band selection studies, and operation plan is described. The ILAS is a solar occultation instrument onboard ADEOS spacecraft with two grating spectrometers: one is for measurement for O3, HNO3, NO2, N2O, H2O, CH4 CFC11 and CFC12 in the infrared band (850-1610cm-1, 11.76µm-6.21m), and another is for aerosols, temperature and air density measurement in the visible band (753-784nm, O2 atmospheric A band). The ILAS will observe the ozone layer over high-latitudes (N55-70, S63-87) regions with a high vertical resolution (2km) for a period of 3 years after launch in 1996.