The aim of this study was to determine the concentrations of air-borne microorganisms (bacteria, fungi, gram negative bacteria (GNB), endotoxins, and respirable suspended particles (RSPs), and their correlation with environmental parameters (temperature, humidity, and carbon dioxide levels) in duck houses. The mean concentrations of bacteria, fungi, and GNB were very high (> $10^6;CFU/m^3$), and endotoxin levels exceeded $10^3;EU/m^3$. Among the various work stages, in the task of receiving ducks, bacteria were $6.2{ imes}10^6;CFU/m^3$, and GNB were $5.4{ imes}10^6;CFU/m^3$, while RSPs levels were $397.6;{mu}g/m^3$ and endotoxin levels were $47.2{ imes}10^3;EU/m^3$ in the task of dividing the ducks, and fungi were $4.9{ imes}10^6;CFU/m^3$ in the task of shipping the ducks. The concentrations of RSPs and endotoxins were significantly higher in tasks involving greater movement of ducks in the house, relative to tasks involving little movement of ducks (p<0.05). Further, with progression in growth of the ducks, the concentrations of bacteria, GNB, endotoxins, and RSPs were significantly increased. There was significant correlation between levels of GNB with bacteria (r=0.75) and fungi (r=0.86), endotoxins with RSPs (r=0.75), bacteria with fungi (r=0.39), and carbon dioxide with RSPs (r=0.38), bacteria (r=0.33), and endotoxins (r=0.31). These results suggest considerable respiratory hazard for farmers in these environments.