Mathematical modelling and effective moisture diffusivity of tomato (Lycopersicon esculentum) was studied during hot air solar drying. An experimental solar dryer with a swivel collector was used for experiments. The collector followed the solar radiation using a precious sensor. Drying experiments were performed in a thin layer hot air drying at slice thicknesses of 3, 5 and 7 mm and air velocities of 0.5, 1 and 2 m/s. The experimental data were fitted to different mathematical moisture ratio models and the Page model was selected as the best model according to correlation coefficient R², chi-square χ² and root mean square error (RMSE) parameters. The maximum values of moisture diffusivity was 6.98 × 10^–9 m²/s at air velocity of 2 m/s and slice thickness of 7 mm while the minimum value of the moisture diffusivity was 1.58 × 10^–9 m²/s at air velocity of 0.5 m/s and slice thickness of 3 mm.