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The inheritance of sulfonylurea (SU) resistance in Monochoria vaginalis was investigated based on the bensulfuron-methyl response phenotypes of F1 plants between SU-resistant (R) and -susceptible (S) and segregation analysis in F2 progenies. Differences of SU resistance between SU-R biotypes and F1 plants at the recommended field dose were also investigated by comparing shoot dry weight. All F1 plants survived the treatment with 25 g a.i. ha−1 bensulfuron-methyl, one-third of the recommended field dose, and showed similar responses to SU-R plants. Conversely, all F1 plants died or showed extreme necrosis at 225 g a.i. ha−1, three times the recommended field dose, as SU-S plants. F2 plants were classified as either R or S phenotype. Segregation for resistance to bensulfuron-methyl in F2 families did not differ from the expected 3:1 (R:S) ratio at 25 g a.i. ha−1. At 225 g a.i. ha−1, the F2 families segregated in a 1:3 (R:S) ratio. These results suggest that SU resistance in M. vaginalis is controlled by a single nuclear allele with resistance being dominant at low dose and susceptibility dominant at high dose. Moreover, F1 plants died or were extremely injured after application of bensulfuron-methyl at the recommended field dose, although SU-R biotypes grew normally. [ABSTRACT FROM AUTHOR]