[en] The object of observation of solar hydrogen Lyman α line (HLy-α 1216 A) is to determine the altitude distribution of oxygen molecular density in the earth atmosphere of 75 km - 150 km high, as HLy-α 1216 A of the solar ultraviolet ray is absorbed a little by molecular oxygen, and reaches the region of about 75 km high. The oxygen density was analyzed with the observation data of absorbing ratio of HLy-α 1216 A in the sky. It is effective to observe HLy-α 1216 A from the viewpoint of ionization in Dlayer as this α line is one of the strongest components of ultraviolet ray in the solar atmosphere. The altitude distribution of oxygen density in the region of 95 - 150 km high is reported here as the result of observing just after sunset. The observation apparatuses consisted of the ionization chamber with the setting angle 110 deg and electric circuit with voltage gain of 160, 80, 40 and 20 times and source voltage 60 V. The K-9M-56 rocket was launched from Uchinoura on Sept. 18, 1976, and this test was successful. The observation results of the flux, solar zenith angle and minimum height in relation to time were obtained, and these data are plotted in the figures. Evaluation was conducted for the oxygen density distribution, the characteristics of ionization chamber, the profile of HLy-α and the level up of observation in the future. (Nakai, Y.)