In a survey conducted in the four major rice ecological zones in Nigeria the predominant weeds of the flora growing in association with both direct‐seeded and transplanted rice(Oryza sativaL.) were determined. Most of the predominant weed species differed with differing rice ecologies. Among the predominant broadleaved species,Ageratum conyzoidesL.,Sphenochlea zeylanicaGaertn,Tridax procumbensL.,Portulaca oleraceaL. andCelosia argenteaL. were each found common to two different ecologies. Also, each of the grass species, includingOryza longistaminataChev and Roehr,Eleusine indica(L.) Gaertn,Digitaria sanguinalis(L.) Scop,Panicum maximumJacq andPanicum repensL. were found in two different ecologies. Of the sedge species,Cyperus rotundusL,Cyperus imbricatusL.,Cyperus difformisL. andFimbristylis dichotoma(L.) Vahl were each found in two different ecologies. The predominant weed species and their relative importance varied with the varying rice ecologies. There was little similarity between the weed communities, indicating that weed species are highly selective in adaptation. Recommending a single herbicide for all the rice ecologies would therefore be most undesirable. The predominant weed species in the various rice ecologies represent potential problems for the present and the future.