Abstract: Leaf area (A_L) of Potamogeton malaianus Miq.in cultivation was estimated using regression and geometric figure fitting methods.The relationships between A_L and cultivation density were investigated. The results were as follows: (1) Leaf length×leaf width was the best parameter to estimate single leaf area, while shoot length×number of leaves on the shoot could predict leaf area of the whole shoot.(2) As cultivation density increased, leaf shape became relatively longer and narrower and SLAincreased, while the average leaf area of shoot decreased.(3) Leaf shape was significantly affected by cultivation densities. Diffe rent combinations of geometric figures were used to model the leaf shapes under different cultivation densities.