About 233 weed species belonging to 54 families mainly occurring in summer were observed in cultivated land and its surrounding area in Cheju Island. The compositae was the most widely occurring family covering 41 weed species, followed by 28 species in gramineae, 14 in labiatae, 13 in leguminasae and 12 in polygonaceae etc.. In terms of the lands classified about 126 species in 39 families were observed in upland ared and 38 species in 20 families occurred in lowland area, 108 species in 36 families in orchard and 214 species in 50 families observed in non-cultivated area. The most dominant weed species in Cheju Island were Portulaca oleracea, Digitaria sanguinalis in both the upland and orchard, Monochoria vaginalis, Cyperus amuricus in lowland, and Digitaria sanguinalis, Artemisia princeps, Partulaca oleracea in non-cultivated land area. There were two communities in upland area, such as Phyllanthus urinaria, Siegesbeckia orinexitalis etc., and Cephalonaplos segetum, Mosla dianthera etc.. The lowland area composed of one major community like Onenanthe javanica, and Eleocharis acicularis. The orchard consisted of the communities of Stellaria aquatics, Viola mandshurica etc., and Justicia procumbens, Varedellia crustacea etc.. The non-cultivated land composed of two major communities like Amplicarpaed edgeworthii, Lactuca indica etc., and Clematis appiiforia, Aster hispidus etc..