The activity of (soluble acid) sucrase was detected in a culture medium of the cell suspension culture of watermelon (Citrullus vulgaris L.). A simple and rapid procedure for the identification and determination of extracellular sucrase from a culture medium of watermelon cell suspension cultures is described. Sucrose was used as a substrate for the determination of extracellular and intracellular activities of the enzyme. Intracellular activity was estimated from the cell suspension. The results show a 91.5–92.0% intracellular and 8.0–8.5% extracellular distribution of sucrase activity. The described method enables to carry out a rapid, simple and specific detection of extracellular sucrase in plants.