Variation in pollen size is prevalent among plant species. This variation also occurs within species. This study looks at the functional role of small and large pollen grains in Ipomoea purpurea. We hypothesize that 1) small pollen grains have an advantage during pollen transport, in that pollinators are likely to carry higher numbers of small pollen grains to a recipient stigma and 2) large pollen grains have a competitive edge over small pollen grains during pollen competition on the stigma. We found that similar quantities of both small and large pollen grains are removed from anthers and deposited onto stigmas by pollinators. However, we found that large pollen grains do sire more seeds than small grains when competing on the same stigma, suggesting that large pollen grains are better competitors. Thus, the question still remains regarding the functional role of small pollen in I. purpurea.