Cells undergo dynamic yet well-coordinated changes in their shape to drive orderly growth and development. Constricting ring (CR) cells of carnivorous fungi can triple in size within 0.1-1 second to capture passing nematodes. However, how the plasma membrane (PM) of ring cells in carnivorous fungus Drechslerella dactyloides accommodates alteration in cell volume during inflation and how this process is regulated remain unknown. We found that newly formed CRs (immature CRs) require a period of maturation to be capable of inflation. During this period, a large number of vesicles accumulate around the inner side of individual ring cells and fuse with others. Strings of fused vesicles subsequently connect with the PM, producing a Palisade-shaped Membrane-building Structure (PMS). The PMS disappeared in both partially and completely inflated ring cells, and the PM of partially inflated ring cells appears wavy and curved, but that of fully inflated ring cells is smooth, suggesting that the PMS serves as a reservoir for membrane-building materials and enables large PM inflation. DdSnc1, a v-SNARE protein, accumulates at the inner side of ring cells during CR maturation and is required for PMS formation and ring cell inflation. The drastic surface expansion of ring cells via the formation of the PMS represents a process distinct from the gradual PM growth via the fusion of individual vesicles in cells undergoing polarized growth.