An improved miniature light bulb socket provided with an insert to keep wire terminals separate. The socket mainly comprises a socket shell in which a Y-shaped insert is seated with two opposed protrusions engaged with the grooves of the socket shell. With such an arrangement the electrical wires and terminals extending into the socket can be kept separate effectively and prevented from their shorting. Further, the socket has a conductor pin disposed on the top of the insert and kept in touch with two electrical wire terminals and so the electrical circuit of a miniature light bulb series can be kept closed even if the light bulb on the socket is burned down. It can have an advantage that the light bulb series can still work even if some bulbs of the light bulb series fail. The improved light bulb socket structure according to the invention indeed enhances the practical value of a socket.