Atmospheric density and pressure in the mesopause region, around 87 km, are inferred using meteor trail ambipolar diffusion coefficient, D, and simultaneously observed airglow OH rotational temperature, TOH. This is the first time to determine the atmospheric density, temperature and pressure by this method. From the 17 nights of data, we found that the number density at around 87 km of altitude varied from 0.9 to 1.2 ¿ 1014 cm-3, and the pressure varied from 0.27 to 0.35 Pascal. The density variation is opposite to the temperature. The OH (6,2) band emission rates showed negative correlation with the density, contrast to positive relation with the temperature. In order to explain temporal variation of the OH emission rate, therefore, it is necessary to assume change of atomic oxygen mixing ratio in the emission heights.