Yield imporovement is one of major breeding objectives of cucumber improvement. Gynoecious, an important agricultural trait which highly correlates with yield, was proved to be controlled by F locus. Conventional plant breeding approach has some limitations in terms of potential inaccuracies and time-consuming. Molecular marker - assisted breeding is, therefore, an effectively alternative solution. F locus– linked molecular marker was previously reported. The main aim of this project was to evaluate the potential applicability of this F locus– specific marker for marker–assisted selection in Vietnam cucumber breeding program. Three different cucumber populations <i>e.g.,</i> pure lines, F2 and F3 population were utilized with 13, 131 and 84 plants, respectively for each population. Plant sexual phenotypes were determined. Sequencing reactions were performed for <I>BCAT</I> 3’UTR of 3 gynoecious and 2 monoecious pure lines. Plant genotypes were determined by standard PCR with a primer pair amplifying a 56 bp-deletion region in <I>BCAT</I> 3’UTR. A 56 bp-deletion was found in <I>BCAT</I> 3’UTR of gynoecious pure lines as compared with monoecious lines. The marker based on this 56 bp-deletion region in <I>BCAT</I> 3’UTR could help to separate cucumber plants having homozygous and heterozygous sex phenotypes. The marker genotype absolutely corresponded with monoecious trait. Especially, the marker could precisely explain for 80 % gynoecious trait. The marker highly explained for Vietnam cucumber sex traits and could be applied for marker-assisted selection in cucumber breeding program in Vietnam in future.