The development of a relationship between microstructural changes of model food products (carrot and potato cubes) and their physical changes during conventional hot air drying (HAD) using combined fractal and image analysis was performed in this study. Dried carrot and potato sections were examined by light microscopy and the fractal dimension (FD) of the microscopic images was determined using a box counting technique. The apparent physical changes of the samples undergoing HAD were represented in terms of the percentage of shrinkage and rehydration ratio. These apparent changes correlated well with their microstructural changes represented by the normalized changes of fractal dimension (Delta FD/FD0) of the microstructural images. Although the microstructural changes of the samples undergoing HAD were quite different, the changes of Delta FD/FD0 of the samples undergoing drying were in the same trend. FD has thus proved to be a good indicator of microstructural changes of products undergoing drying. (c) 2007 Elsevier Ltd. All rights reserved.