The study of pollen grains of Acacia asak showed a marked pollen dimorphism of smooth exine (psilate) polyad type A and rough exine (scabrate) polyad type B, when examined using light microscopy (LM) and scanning electron microscopy (SEM). Typical pollen grains of Acacia asak are 16-monads. Both acetolised and non-acetolised grains of the two types were studied, measured, described and illustrated using LM and SEM. The main differences between these and the functional significance are discussed. Polyad dimorphism can be used as a character to distinguish between A. asak and otherAcacia species. In this study, two polyad types are recorded from the same anther of A. asak for the first time, possibly related to pollination function. However, the function of polyad dimorphism in the same anther is still unclear and requires further study.