The impedance spectroscopy (IS) characteristics of the dual-blue light-emitting diode (LED) and the single-blue LED are measured using a method based on an forward alternating-current (ac) small signal, coupled with atomic force microscopy (AFM) and scanning electron microscopy (SEM) analyses. Experimental results show that both LEDs exhibit the negative imaginary impedance (NII) phenomenon, which is associated with strong radiative recombination intensity. The single-blue LED exhibits a more obvious NII phenomenon compared to the dual-blue LED, because the latter contains a high density of dislocations and local potential barriers that impede the radiative recombination of injected carriers. What’s more, the single-blue LED exhibits smaller parasitic resistances and shorter capacitance relaxation times than the dual-blue LED.