A narrow leaf mutant was obtained after T-DNA transformation conducted on a rice variety Zhonghua 11. Several abnormal morphological characteristics, including semi-dwarf, delayed flowering time, narrow and inward rolling leaves, and lower seed-setting, were observed. The rate of net photosynthesis (un-der saturate light) of flag leaves in the mutant was significantly lower than that of the wild type. More-over, the leaf transpiration rate and stomatal conductance in the mutant flag leaf were lower than those of the wild type at the grain filling stage. It was found that the mutant phenotype was not caused by the T-DNA insertion. Genetic analysis showed that the mutant was controlled by a single recessive gene, designated as nal3(t). A genetic linkage map was constructed using a large F2 mapping population de-rived from a cross between nal3(t) and an indica variety Longtefu B with 6 polymorphic markers on chromosome 12 identified from 366 SSR markers by the BAS method. Gene nal3(t) was mapped be-tween the markers RM7018 and RM3331. Fine mapping of nal3(t) locus was conducted with 22 newly developed STS markers based on the sequence diversity around the region harboring nal3(t) between Nipponbare and 93-11, and nal3(t) was finally mapped to a 136-kb region between the STS markers NS10 and RH12-8. A narrow leaf mutant was obtained after T-DNA transformation conducted on a rice variety Zhonghua 11. Several abnormal morphological characteristics, including semi-dwarf, delayed flowering time, narrow and inward rolling leaves, and lower seed-setting, were observed. The rate of net photosynthesis (un-der saturate light) of flag leaves in the mutant was significantly lower than that of the wild type. More-over, the leaf transpiration rate and stomatal conductance in the mutant flag leaf were lower than those of the wild type at the grain filling stage. It was found that the mutant phenotype was not caused by the T-DNA insertion. Genetic analysis showed that the mutant was controlled by a single recessive gene, designated as nal3 (t). A genetic linkage map was constructed using a large F2 mapping population de-rived from a cross between nal3 (t) and an indica variety Longtefu B with 6 polymorphic markers on chromosome 12 from 366 SSR markers by the BAS method. Gene nal3 (t) was mapped be-tween the markers RM7018 and RM3331. Fine mapping of nal3 (t) locus was conducted with 22 newly developed STS markers based on the sequence diversity around the region harboring nal3 (t) between Nipponbare and 93-11, and nal3 (t ) was finally mapped to a 136-kb region between the STS markers NS10 and RH12-8.