A handrail assembly includes at least one connecting unit, and at least two extension units each connected with the connecting unit. The connecting unit includes a middle tube and two connecting tubes extended from two opposite ends of the middle tube respectively. Each of the connecting tubes has a surface formed with a plurality of elongate slits. Each of the connecting tubes has a periphery formed with an annular reinforcing rib to enhance resilience and fixedness of each of the connecting tubes. Each of the extension units includes a mounting pipe mounted on a respective one of the connecting tubes. Thus, the connecting units and the extension units are detached before assembly to facilitate and reduce the cost of storage, packaging and transportation of the handrail assembly.