This study was conducted to provide data on the weed species composition of the Cyperaceae and Poaceae in the rice fields in An Giang province. The study results show that the weed species composition of Cyperaceae and Poaceae families is very diverse with 38 species belonging to 25 genera, of which 27 are usable. The largest number of species is in crop 1 and in the fields inside the ring dike. Although the species composition is diverse, only a few species are very high frequencies, and most of the remaining species have very low frequencies. Chau Phu district has the highest weed density, averaging 28.42 trees/m2 . Weed density in crop 1 is highest in the 3 crops (15.79 trees/m2 ). Fields outside the ring dike have a higher weed density than paddy fields inside the ring dike (15.37 trees/m2 ). Although crop 1 has more species abundance than crop 3, the species diversity and the species equality in the weed community in crop 1 are lower than crop 3. Rice fields inside the ring dike have higher species abundance than those outside the ring dike, but the indicators H 'and 1 – λ are lower.