Thin-layer solar drying experiments were conducted at Matsuyama, Japan, with medium grain rough rice. The range of average drying air temperature was 22.3-34.9 degreesC, and the relative humidities were between 34.5% and 57.9%. The initial moisture contents were in the range of 37.07-37.69% dry-basis. A mixed-mode natural convection solar grain dryer was used for this experiment. The data of sample weight and dry- and wet-bulb temperatures of the drying air were recorded continuously from morning to evening for each test. The drying data were then fitted to the Page model, biased on the ratios of the differences between the initial and final moisture contents and the equilibrium moisture content (EMC). The model gave a good fit for the moisture content with an average standard error of 0.00387 dry-basis. Both the drying parameters N and K are linear functions of temperature and relative humidity. This single-layer drying equation can be used for the simulation of deep bed drying of rough rice in mixed-mode type natural convection solar dryers. (C) 2000 Elsevier Science Ltd. All rights reserved.