Most soybean cultivars have ovate leaflets, although a few cultivars have narrow or lanceolate leaflets. Narrow leaflet cultivars tend to have more seeds produced per pod than ovate leaflet cultivars, suggesting that the narrow leaflet trait is tightly linked to or cosegregating with the trait controlling number of seeds produced per pod (nspp). The objective of this study was to construct a high resolution map of a chromosomal region controlling narrow leaflet trait and nspp in soybean. A BC3F2 population from a cross between 'Sowonkong' and 'V94-5152' was used. Sowonkong have narrow leaflet and 4-seeded pod and V94-5152 have ovate leaflet and do not have 4-seeded pod. The plants of F2 populations showed a segregation ratio of 3:1 of ovate leaflet to narrow leaflet and then leaflet genotypes were obtained from F2:3 population of each F2 individual. The narrow leaflet-containing plants showed Sowonkong-like pod trait and the ovate leaflet-containing plants V94-5152-like pod trait. The results suggested that, in our mapping population, a single gene controls inheritance of the narrow leaflet character and the narrow leaflet trait is tightly linked to or co-segregating with the trait controlling nspp. Subsequently, we mapped the narrow leaflet locus near Sat_105, Satt270 and SM315 on soybean linkage group I that corresponds with the previously known ln locus. Work is ongoing to construct a fine molecular genetic linkage map on this MLG I region and to find a linkage relationship between ln and nspp. Our results should facilitate further elucidation for the relationship between ln/nspp and yield.