Aims: This study was conducted to investigate the indoor and outdoor air quality at Ashayer Hospital in Khorramabad, Lorestan, Iran, from May-August 2013. Materials and Methods: Air samples were collected using the ZEFON pump (ZEFON factory, USA) based on manufacturer instructions. Bacteria were isolated via differential methods. Diagnosis of fungi was performed based on amount of fungal colonies growth, shapes, colors, pigments, and microscopic procedure. The effects of various environmental factors including temperature, humidity and outdoor bioaerosol levels were also investigated. Results: Staphylococcus spp. were the most predominant isolated bacteria from studied wards. Furthermore, other microorganisms including Streptococcus spp. Corynebacterium spp., and Micrococcus spp. were also isolated from the hospital air. Moreover, the most frequent fungus in indoor environments of hospital was Penicillium spp., while Aspergillusspp. and Alternaria spp. were the next frequent ones. In addition, the most frequent fungi in adjacent outdoors were Penicillium spp., Aspergillus spp., and Cladosporium spp., respectively. No significant difference was found between the mean concentrations of bioaerosols in inside and outside of hospital (P > 0.05). Conclusion: This study suggests that the bioaerosols level in the hospitals were relatively high. Thus, hospitals should enhance practice of good sanitation protocols and infection control measures.