To assess biological indoor air quality in hospital, concentrations of viable airborne microbes were determined at intensive care unit(ICU), patient room (PR), outpatient waiting room(OPWR) in hospitals of large(1000 beds), middle(500 beds), small(100 beds) hospitals, respectively. Gram positive bacteria, gram negative bacteria, fungi were sampled using suctional sampling method by RCS sampler (Reuter centrifugal air sampler) and RCS GK-A agar plate. In gram positive bacteria groups, CNS(Coagulase Negative Staphylococcus), Micrococcus, Lactobacillus, S. aureus, Enterococcus, St. viridans identified. In gram negative bacteria groups, A. baumannii, Kl. peumoniae and E. coli were identified, and Penicillium was identified in fugi groups. Results of the study were as follows. 1. The highest concentrations of airborne microbes was $971CFU/m^3$ at 5:00 PM in small hospital patient room, and average concentrations of airborne microbes in large, middle and small hospitals were $282CFU/m^3$, $289CFU/m^3$ and $625CFU/m^3$, respectively. Average concentrations of airborne microbes in office(control) was $90CFU/m^3$. Thus, the small hospital showed the worst condition. 2. Representatives of 8 different genera were identified in 150 samples. The most frequently isolated organisms were Staphylococcus (73.0%), Micrococcus (20.7%) and Lactobacillus (4.7%), respectively. Pathogenic microbes isolated were A. baumannii, E. coli, Enterococcus, Kl. peumoniae, S. aureus, St. viridans and Penicillium as fungi. In office, no pathogenic microbes were identified. Average concentrations of airborne pathogenic microbes in large, middle and small hospital were $5CFU/m^3$ (2%), $11CFU/m^3$ (4%) and $12CFU/m^3$ (2%), respectively. Thus, condition in a large hospital was better than those in a middle and a small hospital.