The present communication pertains to major weeds of different crop ecosystems of Jorhat in India. The study was based on extensive and intensive fields surveys made during different months of rainy and dry season 2016-2018. Surveys were made in five important crops ecosystems of total eight developmental blocks of Jorhat district during both Kharif and Rabi seasons of the year. Vegetation data were collected followed by quadrat methods and analyzed for density, frequency, diversity and importance value index (IVI) for each crop ecosystems. Interspecific association was also analyzed for ten dominant weed species followed by Cole’s index.  During this period, a total of 82 weed species were reported of which 56 species were recorded from the transplanted Kharif rice fields, while 61 weed species were recorded from the Rabi crop fields. The five dominant weed families in the study area were Cyperaceae, Poaceae, Onagraceae, Asteraceae and Fabaceae.