We have selected 36 schools of a total of night high schools for boys and girls in seoul and measured intensity of illumination of the classroom, The corridors and the stairs that students study and live, with priority given to an illumination, a primary factor of environmental sanitation of school following is the result. 1. The maximum average intensity of illumination of the classroom is 93.2 Lux, and the minimum average intensity of illumination 39.5 Lux. Mean$pm$S, is 59.03$pm$22.8 Lux 2. The maximum average intensity of illumination of the corridor is 39.2 Lux, and the minimum average intensity of illumination 11.1 Lux. 3. The maximum average intensity of illumination of the stair is 11.58 Lux, and the minimum average intensity, of illumination 4.92 Lux, mean$pm$S.D is 7.88$pm$10.0Lux. 4. Schools with tile illumination facilities more than 50 Lux are 63.8% and less than 50 Lux are 36.2%. 5. Schools with 9-11 facilities of a source of light per classroom by a fluorescent lamp are the most as 30.50%. 6. As for the corridor, schools with the illumination equipment less than 10 Lux are 27.8%, are more than 10 Lux 72.2% 7. As for the stairs schools with the illumination equipment less than 10 Lux are 77.8%, and more than 10 Lux 10 Lux 22.2%.