Background: Air pollution, both indoor and outdoor, is often considered as one of the major causes of environmental health problems. Usually, air in slaughterhouses is heavily contaminated by large quantities of dust particles of biological and nonbiological origin, toxic gases, and odors. However, the quality of indoor air in slaughterhouses was rarely investigated. Objective: To evaluate the slaughterhouse indoor environment parameters such as particulate, toxic gases, and bioaerosol levels. Materials and Methods: Indoor and outdoor air quality parameters CO, O3, CO2, VOCs, PM10, PM2.5, SO2, and NO2 were measured using references calibrated air sampling devices. Microbial air samples were taken using Staplex air sampler. To assess indoor air quality in Dammam slaughterhouse, air samples were taken from two different laboratories. Result: All mean levels of CO2 inside all slaughterhouse laboratories were higher than their AQG value, which is recommended by the World Health Organization and in Europe. Indeed, the average levels of NO2 and CO were lower than their AQGs. However, the mean levels of SO2 and VOCs were significantly exceeding the air quality guidelines. Bioaerosols examination using Staplex air sampler indicated that limited number of bacterial and fungal strains contaminate slaughterhouse air in the two laboratories. In comparison with laboratory A, the 44.2% reduction in total viable bacterial count, as compared with laboratory B, reflected the better hygienic standards followed in this new laboratory. Colony count remains constant after 5 and 10 min with approximately 25 CFU/m3 near director’s offices due to limited working activities. Conclusion: Location of slaughterhouse close to second industrial city of Dammam was significantly having serious impact up on indoor and outdoor air quality data. Indeed, slaughterhouses environment should be controlled for bioaerosol production and bacterial contaminations through good and efficient ventilation system.