LSI Technology is experiencing a steady development from half micrometers to quarter micrometers generations. With this development, quality control is becoming more severe. Therefore, the level of quality required for dust proof pellicles is getting higher. As the line width of devices narrows, the quality and function of pellicles by the conventional method has become insufficient. In order to cope with the finer line width, the influence of clean room environments on pellicles should be understood, and some cautions should be noted. In this paper, three issues of the environmental influence are discussed. For each issue, its nature, possible adverse effects, and some recommendations are presented respectively.