The present study was conducted in Morikhaboloo beel(Wetland) of River Subansiri, Assam to evaluate the macrophytic diversity of the wetland for a period of one year i.e. from August2013 to July 2014. During the present investigation found a distinct seasonal variation in the distribution of macrophytes: based on importance value index, Eichhornia crassipes (Mart.), Ceratophyllum demursum L. and Trapa quadrispinosa Roxb. were dominant in the summer; E. crassipes and Hydrilla verticillata (L.f.) Royle were dominant in the winter; and Ceratophyllum submersum L., H. verticillata, E. crassipes and L. hexandra were dominant in the spring. The highest species diversity was observed in the summer, followed by winter and then spring. The luxuriant growth of aquatic macrophytes evinced the highly productive nature of the wetland, while the dominance of emergents among the growth forms indicates the encroachment of littoral vegetation, indicating a successional trend toward marsh meadow. Different diversity indices like Shannon-Weaver diversity index, Simpson diversity index, Menhinick diversity index, and Concentration of dominance were calculated among 61 species to show the plant communities structure of the wetland. Maximum values of Shannon- Weaver diversity index, Simpson diversity index and Menhinick diversity index were found during the summer season as it is active growth period of macrophytes whereas maximum concentration of dominance during the summer season reflects the dominance of few species due to high diversity of the macrophytes.