Alternanthera philoxeroides has expanded distribution from late 1990s in paddy fields of Inba-numa area. We investigated the quantity of distribution in each per cell in the paddy field in the Moroto river basin for the grasp of the distribution realities and the clarification of the diffusion factor for 2008-2009 years. As a result, the distribution of the Alternanthera philoxeroides was confirmed a lot in not only paddy field but also Levee in Inbanuma area. It was suggested that the important factor of the diffusion is the distance from the farm where Alternanthera philoxeroides was distributed over in last year and the distance from the irrigation canal.