Silicon photonics has been longing for an efficient on-chip light source that is electrically driven at room temperature. Microdisk laser featured with low-loss whispering gallery modes can emit directional lasing beam through a closely coupled on-chip waveguide efficiently, and hence is particularly suitable for photonics integration. The realization of electrically pumped III-nitride microdisk laser grown on Si has been impeded by the conventional undercut structure, poor material quality, and a limited quality of GaN microdisk formed by dry etching. Here we report a successful fabrication of room-temperature electrically pumped InGaN-based microdisk lasers grown on Si. A dramatic narrowing of the electroluminescence spectral line-width and a clear discontinuity in the slope of light output power plotted as a function of the injection current provide an unambiguous evidence of lasing. This is the first observation of electrically pumped lasing in InGaN-based microdisk lasers grown on Si at room temperature.