At the BACUS Symposium held in Santa Clara in 1993, we made a presentation on pellicles for KrF Excimer (including UV-II) stepper based on our development activities. In this presentation, among other issues, we pointed out that compound vapors in the clean room environment influence longevity of the membrane made of fluoropolymer. However, a series of tests, which the presentation was based upon, were carried out by using approximately 2,000 times stronger beam intensity than the actual stepper beam intensity. Ideally, the tests should have completed by applying actual stepper beam intensity ; however, it would take at least 6 months to one year to complete one test, and therefore, this method is not practical. This time, we have applied Kinetic theory analysis to light resistance of KrF Excimer pellicle under stepper's laser exposure conditions.