The ultimate goal of this research was to develop a semi-continuous flow grain treatment system and predictive model that will reduce microorganisms on grain kernel surfaces with ozone. The focus of this research was to determine the concentration-time product (CTP) of ozone required to eliminate various levels of microbial growth on grain kernels. To examine the effect of ozone on surface microbes, samples of freshly-harvested and stored maize were treated with ozone for 1 and 3 hours at average ozone concentrations of 1752 ppm, 915 ppm and 37 ppm. Microorganisms were significantly decreased by 28 to 57% after maize samples were ozonated for 1 h at 37 to 1752 ppm and 45 to 80% for 3 h at 37 to 1752 ppm. Linear regression analysis of the CTP data indicated that percent mold reduction increased at a rate of 0.0088 times the CTP. The modified Gompertz equation applied to the microbial inactivation data indicated that a 0.5 to ~1 log mold reduction on maize kernels was attained for ozone concentrations between 37 and 1752 ppm. When compared to preliminary field data from a semi-continuous flow grain treatment system, the laboratory data and the model-predicted values were reasonably close with respect to the microbial load reduction observed on maize samples taken from the system.