To assess microbiological indoor air quality in schools, concentrations of viable airborne microorganisms were monitored at classrooms and corridors of 3 middle or high schools in Ulsan. Airborne microorganisms were sampled at various situations during a semester (class-hour, lunchtime, after school) and during a vacation with an impaction-type air sampler. During the semester, the number of bacteria was the highest at lunchtime in corridor with an average of $1,111;MPN/m^{3}$ and lowest at class-hour in corridor with an average of $132;MPN/m^{3}$. During the vacation, the bacterial concentrations at classrooms and corridors were only $5{\%}$ and $27{\%}$ of the values during class-hours of the semester, respectively. Among the colonies tested, $60{\%}$ were identified as relatively harmless Micrococcus species and $12{\%}$ were Staphylococcus species. During the semester, the average values of fungal concentrations at each situation ranged from 105 to $213;MPN/m^{3}$, and the values during the vacation were $32;MPN/m^{3}$ at classrooms and $83;MPN/m^{3}$ in corridors. Fungal genera such as Cladosporium, Penicillium, and Aspergillus were identified from the colonies. The obtained data can be considered as a step to set a guideline for bioaerosols in indoor environment of schools.