Abstract: A bicycle handlebar assembly includes a handlebar, two auxiliary bars, two supporting assemblies and two positioning assemblies. The two auxiliary bars are assembled on the handlebar. Each auxiliary bar has a plurality of first holes and a plurality of second holes corresponding to the first holes. The two supporting assemblies are mounted on the two auxiliary bars respectively. The two positioning assemblies are disposed to the two auxiliary bars and the handlebar. Therefore, each supporting assembly and the respective auxiliary bar are secured on the handlebar via the respective positioning assembly. Furthermore, each supporting assembly and the respective auxiliary bar are adjustable via the first and second holes.