Lallemantia royleana is a mucilaginous endemic plant which is growing in different regions of European and Middle Eastern countries, especially in Iran. This seed contains a large amount of mucilaginous gum with inherent capacity for being used instead of the present commercial gums. An optimized aqueous extraction process is used for the removal of the mucilage from the whole seed. At the preparation steps of extraction process, the seeds are swollen and the size increasing can be evaluated as a yield extraction criterion. However, the sticky mucilage presented on these seeds cause major difficulties in dimension measurement. In the present study, the seed size variation as a function of extraction parameters (temperature and water/seed ratio) were investigated using the image analysis technique. A mathematical model was also developed and shown to fit the mucilage layer thickness during water sorption.