The thin layer solar drying experiments of organic tomato using solar tunnel dryer were conducted under the ecological conditions of Ankara, Turkey. During the experiments, organic tomatoes were dried to the final moisture content of 11.50 from 93.35% w.b. in four days of drying in the solar tunnel dryer as compared to five days of drying in the open sun drying. Experimental drying curves showed only a falling drying rate period. A non-linear regression procedure was used to fit 10 different thin layer mathematical models available in literature to the experimental drying curves. The models were compared using the coefficient of determination, mean relative percent error, root mean square error and the reduced chi-square. The approximation of diffusion model has shown a better fit to the experimental drying data as compared to other models. The effect of the drying temperature and relative humidity on the drying model constant and coefficients were also determined. Samples dried in the solar tunnel dryer were completely protected from insects, rain and dusts, and the dried samples were of high quality in terms of colour and hygienic. This system can be used for drying various agricultural products. Also, it is simple in construction and can be constructed at a low cost with locally obtainable materials. (c) 2005 Elsevier Ltd. All rights reserved.