A rail terminal assembling structure includes a protection member formed with an assembling passage defined by a contact side section, a connection side section and two lateral sections. The connection side section has a first locating section, an elastic locating section and a second locating section. An end section of a conductive plate extends into the assembling passage and securely attached to the contact side section. A metal leaf spring has a first section, a second section and an elastic bight section connected between the first and second sections. The first section has a first located section and an insertion section. When the first section extends into the assembling passage and the first section elastically pushes/presses the elastic locating section until the insertion section reaches the elastic locating section, the elastic locating section is elastically engaged with the insertion section.