We study a solar eruptive prominence with flare/coronal mass ejection (CME) event by microwave and extreme ultraviolet (EUV) observations. Its evolution can be divided into three phases: slow rise, fast expansion, and ejection. In the slow-rise phase, the prominence continuously twists for more than one hour with a patch of bright emission appearing around the top. When the north leg interacts with the local small-size loops, the fast expansion is initiated and the flare takes place there. The prominence grows rapidly, and a series of localized brightenings appear in the whole prominence structure. Then the ejection occurs, followed by a CME. In microwave images, the brightness temperature (T b ) at 17 and 34 GHz can be divided into three components. The strongest emission with T b at 25,000─300,000 K is related to the bright flare region near the north foot. The medium T b (10,000─20,000 K) outlines a series of small-scale bright enhancements scattering in the prominence, which are superposed on a weak background with T b at 5000─10,000 K. These localized bright structures, first appearing at the top and then scattering in the entire prominence structure, are cospatial with EUV bright threads, fibers, or spots in both high- and low-temperature passbands. They display significant temporal variations on the scale of 3─5 s in the microwave observations. Thus, the plasma inside the prominence is spatially structured and changes with time in both density and temperature. This behavior could be interpreted in the frame of the small-scale and short-term process of energy releases in the twisted magnetic structure.