The ability to initiate stem elongation at the early growth stages of a plant is the major survival mechanism of floating rice in the presence of flooding. We previously identified two quantitative trait loci (QTLs) for this “early elongation ability” on chromosomes 3 and 12 using a Patnai23 (a non-floating cultivar) × Goai (a floating cultivar) F₂ population. The objectives of the present study were: (1) to identify QTLs for early elongation ability in the cross Habiganj Aman VIII (a floating cultivar) × Patnai23, and (2) to confirm the results obtained in our previous diallel analysis indicating that Habiganj Aman VIII might harbour additional gene(s) for early elongation ability compared with Goai. The genotype of a total of 192 F₂ plants was investigated using 85 (9 RFLP and 76 SSR) markers and the plants were assessed for early elongation ability. We scaled early elongation ability based on the position of the lowermost internode that exhibited elongation (“lowest elongated internode”, LEI), since the LEI position parallels the time of the onset of stem elongation. As a result, a large QTL detected on chromosome 12 seemed to be common to the two crosses. A small QTL detected on chromosome 1 was unique to the Habiganj Aman VIII × Patnai23 cross, which was consistent with the results obtained in our previous diallel analysis. No QTLs were found on chromosome 3 in this cross. These results suggested that (1) the QTL on chromosome 12 might be the most important one for the expression of early elongation ability in terms of the to percentage of phenotypic variation and consistency in different backgrounds, and (2) diallel analysis might be an effective method for examining differences in genetic control among diverse parents.