Paraquat (1,1'-dimethyl-4,4'-bipyridinium) tolerance is an important trait in the weed control during crop production. The paraquat tolerant (Pq72) and susceptible (Pq1192) mutants are pure lines derived from the mutation pool of rice cultivar TNG67. Two reciprocal crosses, Pq72/Pq1192 and Pq1192/Pq72, were conducted between Pq72 and Pq1192 mutant lines for studying the genetic of paraquat tolerance by investigations of physiological characteristics related to paraquat tolerance including leaf injury index, leaf chlorophyll fluorescence (Fv/Fm) and electrolyte leakage in the F 2 populations of two reciprocal crosses after paraquat treatment. The results suggested that a maternal inheritance of paraquat tolerance is existed in these mutants. Further analysis found that the F 2 population of Pq72/Pq1192 segregated 3:1 (tolerant to susceptible) in both Fv/Fm and electrolyte leakage, respectively. This result implies that the paraquat tolerance of the Pq72 mutant is controlled by a single dominant gene.