Individual microdisk blue-light-emitting diodes (μ-LEDs) of varying diameters from 5 to 20 μm have been fabricated from InGaN/GaN quantum wells. Size effects on the μ-LED characteristics, including I-V and L-I characteristics, have been measured. The transient behavior of the μ-LEDs has also been studied. It was found that the turn-on time is on the order of our system response (30 ps) and the turn-off time is on the order of 0.2 ns and shows a strong size dependence. The ability of two-dimensional array integration with advantages of high speed, high resolution, low temperature sensitivity, and applicability under versatile conditions make III-nitride μ-LEDs a potential candidate for light sources in short-distance optical communications.