An improved structure of inductor includes a C-shaped core and a prismatic strut core. The C-shaped core has two extended portions and a side portion that has its two ends connected to a fixed end of each of the extended portions. The prismatic strut core has a bottom surface, a top surface, and a number of side surfaces that are wound around by a coil. The prismatic strut core inserts and places between the two extended portions with the coil pressed against the side portion. When it comes to assembling, all one has to do is to place the prismatic strut core into the C-shaped core and has adhesive to glue the coil to the side portion to complete the fabrication of the inductor in order to prevent the coil from being loose and come off.