This study aimed to determine the aeration rate and its kinetics in aerobic composting of agricultural wastes. For this aim compost materials were prepared by mixing grass trimmings, tomato, pepper, and eggplant wastes. Four vertical forced aeration type reactors and one vertical natural convection type reactor were manufactured to apply four different aeration rates. CO2 rate and temperature changes were recorded in three different places in the reactors. Moisture content, pH and organic material rate were recorded each day. While process-monitoring parameters (CO2, temperature, pH, moisture content) were used for interpretation of the process, organic material degradation was used for interpretation of the process success. The seven different kinetic models were applied for modeling decomposition rate to the experimental values. According to the results, four of these models were found applicable to this study. These models were analyzed with some statistical methods as root mean square error (RMSE), chi-square (chi(2)), and modeling efficiency (EF). According to the statistical results of these models, the best model was found as: k(T) = aMe/T-(C(.)b).exp ([T(.)c)-(d.Me/T)] where k(T) is the rate of decomposition (g VS/g VS day); T the process temperature (degreesC; M-e the daily moisture content (%wb); C the daily CO2 rate in composting reactor (%) and a, b, c, d are constants. According to the results, the highest organic matter degradation and temperature value were obtained at the aeration rate of 0.41 air min(-1) kg(om)(-1). Thus, it could be applied to this mixed materials composting process. (C) 2003 Elsevier Ltd. All rights reserved.