The objective of this research was to identify mould in university’s library using cross sectional design. The existence of mould and physical and chemical quality of air in library have been investigated and observed in three faculties; they were in FA, FB, and FC. To identify the mould, it used petri dish in Potato Dextrose Agar medium. There were 6-9 samples from each library. The temperature in three libraries were higher than standard, the intensity of light were very low in location FB and FC, and the dust concentration in FA was very high. It was found the pathogenic mould; they were Aspergillus fumigatus in FA, Scopulariopsis candida in FB, and Fusarium verticilloides in FC. In general, the physical, chemical and microbial quality of air in libraries exceeded the legal standard.