Abstract: Pollen wall structure and adenosine triphosphatase in pollen grains of Citrullus lanatus was studied ultrastructurally. The exine of pollen wall is of different electron density, the nexine dense and the sexine, comprising tectum, bacules, and foot layer, relatively thin. There is some space between sexine and nexine. Product of ATPase reaction was mainly found in plastid, ERs, matrix of cytopla sm, and intine of pollen wall.