This study presents a numerical evaluation of air flow and odor emission rate from an open manure storage tank. Odor emission rate is needed to facilitate the odor dispersion study and to compare different odor sources in terms of odor emission. The concentration at the manure surface, the tank dimensions, and wind speed were used to calculate air flow and the emission rate. The SIMPLER algorithm developed by Patankar (1980) and a two-layer turbulence model were used in the numerical simulation with a grid of 152 ¥ 139. The predicted emission rate agreed with the field measurement results found in the literature. Experimental verification of the air flow showed that the flow pattern and velocity profile prediction were also in agreement with the experimental results. The calculated odor-emission rate was a function of the manure surface area, the odor concentration at the manure surface, the tank dimensions, and the wind speed.