Bioethanol has attracted more attention as a clean-burning fuel that can benefit both environment and energy sector. Gooseweed and small-flowered nutsedge are abundant in rice fields in form of weeds and considered as a major agricultural problem. Thus, this paper aims to evaluate the possibility of ethanol production from these two weeds by calculating the theoretical ethanol yield from its reducing sugars and cellulose content. Experiment was conducted in rice fields in Chiang Mai province, Thailand and 207 kg/ha and 201 kg/ha biomass yield was obtained from gooseweed and small-flowered nutsedge plants. The theoretical ethanol yield of gooseweed and small-flowered nutsedge were 160 L/Mg and 223 L/Mg, respectively that suggest utilizing these materials as promising feedstocks for bioethanol production.